Almost. Strings are NUL terminated, so you probably want to allocate an extra byte to store the NUL byte. That is, even though sides is 1 character long, it really is 2 bytes: {5,'\0'}.

So it would be:

tempSides = (char *)malloc((strlen(sides)+1)*sizeof(char));

and if you wanna copy it in:

strcpy(tempSides, sides);
Answer from Claudiu on Stack Overflow
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codestudy
codestudy.net โ€บ blog โ€บ memory-allocation-char-and-char
Memory Allocation in C: char* vs char[] โ€“ What's the Difference?
It stores the memory address of a single char or the first element of a character sequence (string). Unlike char[], char* itself is just a pointer variableโ€”it does not own the memory it points to.
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c - Memory allocation for char array - Stack Overflow
You are responsible for (1) preserving a pointer to the beginning address of the memory block (so it can be freed later); and (2) freeing the memory when you are done with it. A simple example will help. Most of the memory allocation/free functions are declared in stdlib.h. char *name = NULL; ... More on stackoverflow.com
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sizeof Char / Array length Memory allocation in C, - Stack Overflow
Can somebody tell me about the memory allocation in c? What is the size of a char variable? 2 or 4? Why the difference in the address value between 2 neighboring char elements in an array is only 1? More on stackoverflow.com
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c - Char memory allocation - Stack Overflow
Connect and share knowledge within a single location that is structured and easy to search. Learn more about Teams ยท Get early access and see previews of new features. Learn more about Labs ... I am writing a program that reads a user input, but I don't want to give any upper limit to it's size, so I've decided to allocate it's memory dynamically like this: int main(int argc, char ... More on stackoverflow.com
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c - Dynamic memory allocation with char - Stack Overflow
But for some reason the code above give me an "Invalid read of size 1" at strlen(). ... not very efficient. Do you have an upper bound or perhaps realloc in chunks of a 1k?Also avoid the repeated use of strlen ... Worked with i+2. Thank you! ... strlen will not determine the size of the allocated char ... More on stackoverflow.com
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r/C_Programming on Reddit: Memory allocation for char array inside struct
July 28, 2018 -

Hey friends,

I'm sure somebody on the internet jas alread answered this, but I honestly haven't found a suitable answer for me.

Let's say we have a struct like this:

typedef struct {
    char *name;
    int age;
} Human;

And a kind of "constructor" function like this:

Human *human_new(char *name, int age)
{
    Human *this = (Human *) malloc(sizeof(Human));

    this->name = name;
    this->age  = age;

    return this;
}

My question is, do I need to allocate memory for the char pointer name of the struct or is the assignment of this->name enough?

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1 of 5
25
My question is, do I need to allocate memory for the char pointer name of the struct or is the assignment of this->name enough? Depends on what you want to do. If you simply assign to this->name, then the object you've just allocated won't "own" the pointer or the contents of the string to which it points. It has merely borrowed the pointer. The string contents could change at any time, or the pointer could be invalidated by being freed, without the Human object even knowing. Borrowing pointers can indeed be useful in some cases, but it's almost certainly not what you want here. You probably want to strdup the name argument to create a completely new string with the same contents. You might even want to change name to be a const char *, to emphasise the fact that the value being passed is going to be copied, not borrowed. If you do create a whole new string for that name field, you will probably want to provide a destructor for your Human objects, e.g.: void human_free(Human *this) { free(this->name); free(this); } Also, on a completely different note, the cast in: Human *this = (Human *) malloc(sizeof(Human)); isn't necessary in C. Object pointers can be converted to and from void pointers without casts.
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Yes, you will need to allocate memory for whatever you want to put in the name of the struct. malloc(sizeof(Human)) will allocate enough space for a char pointer and an int, it won't allocate memory for the contents of name because it has no idea what the size will be. If you know the upper bound on the size of name, or are happy to enforce one, you could change the definition of the struct to: typedef struct { char name[100]; int age; } Human; Then when you call malloc(sizeof(Human)) you'll get enough space for a 'string' containing up to 100 characters (only 99 usable because of the null terminator) and an int. If you do that, it would probably be sensible to define the maximum length of a name as #define MAX_HUMAN_NAME_LENGTH 100 to be clearer and so you only have to change it in one place.
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LabEx
labex.io โ€บ tutorials โ€บ c-how-to-manage-memory-for-char-types-in-c-510337
How to manage memory for char types in C | LabEx
A char typically occupies 1 byte of memory, which can represent 256 different values (0-255). This makes it ideal for storing ASCII characters and small integer values. graph LR A[Memory Allocation] --> B[1 Byte] B --> C[0-255 Possible Values]
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48

Declaring Static Character Arrays (strings)

When you know (or have a reasonable idea how large your array needs to be, you can simply declare an array of sufficient size to handle your input (i.e. if you names are no longer than 25 characters, then you could safely declare name[26]. For strings, you always need at minimum the number of chars to store + 1 (for the null-terminating character).

If there may be a few characters more than 25, there's nothing wrong with declaring your array few bytes longer than needed to protect against accidental writing beyond the end of the array. Say name[32].

Let's declare an array of 5-characters below and look at how the information is stored in memory.

char name[5] = {0}; /* always initialize your arrays */

The above declaration creates an array of 5-contiguous bytes on the stack for your use. e.g., you can visualize the 5-bytes of memory initialized to zero as follows:

        +---+---+---+---+---+
 name   | 0 | 0 | 0 | 0 | 0 |
        +---+---+---+---+---+
          \
           'name' holds the starting address for
            the block of memory that is the array
            (i.e. the address of the first element
             like: 0x7fff050bf3d0)

Note: when using name to hold a 'character string', the actual string can be no longer than 4 chars because you must end a sting with a null-terminating character, which is the null-character '\0' (or simply numeric 0, both are equivalent)

To store information in name, you can either do it by assigning characters one-at-a-time:

name[0] = 'J';
name[1] = 'o';
name[2] = 'h';
name[3] = 'n';
name[4] =  0;   /* null-terminate. note: this was already done by initialization */

In memory you now have:

        +---+---+---+---+---+
 name   | J | o | h | n | 0 |    /* you actually have the ASCII value for */
        +---+---+---+---+---+    /* each letter stored in the elements    */

Of course, nobody assigns one character at a time in this manner. You options are many, using one of the functions provided by C, e.g. strcpy, strncpy, memcpy, or by reading information from a file stream, or file descriptor with fgets, getline, or by using a simple loop and index variable to do the assignment, or by using one of the string formatting functions, e.g. sprintf, etc... For example you can accomplish the same thing with any of the following:

/* direct copy */
strcpy (name, "John");
strncpy (name, "John", 5);
memcpy (name, "John", sizeof "John");  /* include copy of the terminating char */

/* read from stdin into name */
printf ("Please enter a name (4 char max): ");
scanf ("%[^\n]%*c", name);

Note: above with strncpy, if you had NOT initialized all element to 0 (the last of which will serve as your null-terminating character, and then used strncpy (name, "John", 4); you would need to manually terminate the string with name[4] = 0;, otherwise you would not have a valid string (you would have an unterminated array of chars which would lead to undefined behavior if you used name where a string was expected.)

If you do not explicitly understand this STOP, go read and understand what a null-terminated string is and how it differs from an array of characters. Seriously, stop now and go learn, it is that fundamental to C. (if it doesn't end with a null-terminating character - it isn't a c-string.

What if I don't know how many characters I need to store?

Dynamic Allocations of Character Strings

When you do not know how many characters you need to store (or generally how many of whatever data type), the normal approach is to declare a pointer to type, and then allocate a reasonably anticipated amount of memory (just based on your best understanding of what you are dealing with), and then reallocate to add additional memory as required. There is no magic to it, it is just a different way of telling the compiler how to manage the memory. Just remember, when you allocate the memory, you own it. You are responsible for (1) preserving a pointer to the beginning address of the memory block (so it can be freed later); and (2) freeing the memory when you are done with it.

A simple example will help. Most of the memory allocation/free functions are declared in stdlib.h.

char *name = NULL;  /* declare a pointer, and initialize to NULL */

name = malloc (5 * sizeof *name); /* allocate a 5-byte block of memory for name */

if (!name) {    /* validate memory was allocated -- every time */
    fputs ("error: name allocation failed, exiting.", stderr);
    exit (EXIT_FAILURE);
}

/* Now use name, just as you would the statically declared name above */
strncpy (name, "John", 5);

printf (" name contains: %s\n", name);

free (name);    /* free memory when no longer needed.
                   (if reusing name, set 'name = NULL;') 
                 */

Note: malloc does NOT initialize the contents of the memory it allocates. If you want to initialize your new block of memory with zero (as we did with the static array), then use calloc instead of malloc. You can also use malloc and then call memset as well.

What happens if I allocate memory, then need More?

As mentioned above discussing dynamic memory, the general scheme is to allocate a reasonable anticipated amount, then realloc as required. You use realloc to reallocate the original block of memory created by malloc. realloc essentially creates a new block of memory, copies the memory from your old block to the new, and then frees the old block of memory. Since the old block of memory is freed, you want to use a temporary pointer for reallocation. If reallocation fails, you still have your original block of memory available to you.

You are free to add as little or as much memory as you like at any call to realloc. The standard scheme usually seen is to start with some initial allocation, then reallocate twice that amount each time you run out. (the means you need to keep track of how much memory is currently allocated).

To sew this up, let's end with a simple example that simply reads a string of any length as the first argument to the program (use "quotes" if your string contains whitespace). It will then allocates space to hold the string, then reallocate to append more text to the end of the original string. Finally it will free all memory in use before exit:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main (int argc, char **argv) {

    if (argc < 2) { /* validate input */
        fprintf (stderr, "error: insufficient input.  usage: %s \"name\"\n",
                 argv[0]);
        return 1;
    }

    size_t len = strlen (argv[1]);  /* length of input  */
    size_t sz_mem = len + 1;        /* memory required  */

    char *name = malloc (sz_mem * sizeof *name);  /* allocate memory for name */

    if (!name) {    /* validate memory created successfully or throw error */
        fputs ("error: name allocation failed, exiting.", stderr);
        return 1;
    }

    printf ("\n allocated %zu bytes of memory for 'name'\n", sz_mem);
    memset (name, 0, sz_mem); /* initialize memory to zero (optional) */

    strncpy (name, argv[1], sz_mem);  /* copy the null-terminator as well */
    printf (" name: '%s' (begins at address: %p)\n", name, name);

    /* realloc - make name twice as big */
    void *tmp = realloc (name, 2 * sz_mem);  /* use a temporary pointer */
    if (!tmp) {                              /* check realloc succeeded */
        fprintf (stderr, "error: virtual memory exhausted, realloc 'name'\n");
        return 1;
    }
    memset (tmp + sz_mem, 0, sz_mem * sizeof *name); /* zero new memory */
    name = tmp;         /* assign new block to name       */
    sz_mem += sz_mem;   /* update current allocation size */

    printf (" reallocated 'name' to %zu bytes\n", sz_mem);
    strncat (name, " reallocated", sizeof " reallocated");

    printf ("\n final name : '%s'\n\n", name);

    free (name);

    return 0;
}

Use/Output

$ ./bin/arraybasics "John Q. Public"

 allocated 15 bytes of memory for 'name'
 name: 'John Q. Public' (begins at address: 0xf17010)
 reallocated 'name' to 30 bytes

 final name : 'John Q. Public reallocated'

Memory Check

When you dynamically allocate memory, it is up to you to validate you are using the memory correctly and that you track and free all the memory you allocate. Use a memory error checker like valgrind to veryify your memory use is correct. (there is no excuse not to, it is dead-bang-simple to do) Just type valgrind yourprogramexe

$ valgrind ./bin/arraybasics "John Q. Public"
==19613== Memcheck, a memory error detector
==19613== Copyright (C) 2002-2012, and GNU GPL'd, by Julian Seward et al.
==19613== Using Valgrind-3.8.1 and LibVEX; rerun with -h for copyright info
==19613== Command: ./bin/arraybasics John\ Q.\ Public
==19613==

 allocated 15 bytes of memory for 'name'
 name: 'John Q. Public' (begins at address: 0x51e0040)
 reallocated 'name' to 30 bytes

 final name : 'John Q. Public reallocated'

==19613==
==19613== HEAP SUMMARY:
==19613==     in use at exit: 0 bytes in 0 blocks
==19613==   total heap usage: 2 allocs, 2 frees, 45 bytes allocated
==19613==
==19613== All heap blocks were freed -- no leaks are possible
==19613==
==19613== For counts of detected and suppressed errors, rerun with: -v
==19613== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 2 from 2)

In the output, the following lines are of particular significance:

==19613== HEAP SUMMARY:
==19613==     in use at exit: 0 bytes in 0 blocks
==19613==   total heap usage: 2 allocs, 2 frees, 45 bytes allocated

This tells you that all memory allocated during your program has been properly freed. (make sure you close all open file streams, they are dynamically allocated as well).

Of equal importance is the ERROR SUMMARY:

==19613== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 2 from 2)

There are no errors in the memory use. If you attempt to read, write or free memory from a location outside your block, or from an unitialized location or that would leave other memory unreachable, that information will show as an error.

(the suppressed: 2 from 2 just relate to additional debug libraries not present on my system)

This ended up longer than intended, but if it helps, it was worth it. Good luck.

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5

How can I announce the array and then define it's size?

Don't; 'announce' it when you know what size it needs to be. You can't use it before then anyway.

In C99 and later, you can define variables when needed โ€” anywhere in a statement block. You can also use VLAs (variable-length arrays) where the size is not known until runtime. Don't create enormous arrays as VLAs (e.g. 1 MiB or more โ€” but tune the limit to suit your machine and prejudices); use dynamic memory allocation after all.

If you're stuck with the archaic C89/C90 standard, then you can only define variables at the start of a block, and arrays have sizes known at compile time, so you have to use dynamic memory allocation โ€” malloc(), free() etc.

Top answer
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3

You are not printing addresses correctly: an address is not an int, so you cannot use %d to print it. Use %p (for "pointer") instead, and cast the address to void* for printing:

printf ("This is the Address of val1 %p\n", (void*)&foo[1]);

Now your program produces this or similar output:

This is the Address of val1 0xffbd2fcf 
This is the Address of val2 0xffbd2fd0 
The size of each array member is 2

Two pointers are off by 1, which is the size of a single char. The size of the entire array is 2. If you want to print the size of a single element, use foo[0].

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0

Memory Allocation is a bit tricky, but it's easier than you think. It is, as the name implies, the usage and selection of data to optimize program function and speed. Basically, Memory Allocation is a "perk" of languages such as C/C++ that allow programmers to only use EXACTLY as much data as needed, freeing up memory for other computer functions.

Some good info to know about memory...

  • memory is known in "bytes", these are 8-bit "groups" of data.
  • A "bit" is a value that is either 0 or 1.

Variable sizes:

  • Char: 1 byte
  • Int: 4 bytes
  • double: 8 bytes

When neighboring elements are of the same type (for example, an array of chars), they will have a difference in address that increments/decrements by the value of the memory size. Since a char variable has a size of 1 byte, neighboring elements will have addresses that differ by 1.

Ex: char addresses: 1204, 1205, 1206, 1207... (1 byte)

int addresses: 1204, 1208, 1212, 1216... (4 bytes)

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Code Quoi
codequoi.com โ€บ en โ€บ malloc-allocating-memory-in-c
Malloc: Allocating Memory in C - codequoi
With the malloc (memory allocation) function, we can ask the operating system to allocate a memory area of a certain size in the heap. To use it, we must include the stdlib.h library as follows: ... Malloc returns a void pointer (which can be interpreted as any other type or data), and takes ...
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Medium
csnotes.medium.com โ€บ malloc-in-c-for-int-and-char-c3677b857b65
Malloc in C, for int * and char * | by zihan | Medium
May 15, 2021 - We first allocate memory vertically, to know how many rows we need. char **file; file = (char **)malloc(sizeof(char *) * (size + 1)) First, we tell the program how many lines we want our file to have. Each line is a string (char *, see Case 2). After we allocate memories for the number of lines we want AND we add the NULL-terminator at the end (very important, donโ€™t forget!), we can allocate memory horizontally for each of these lines.
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Physics Forums
physicsforums.com โ€บ other sciences โ€บ programming and computer science
C: How to allocate memory for char*** data type โ€ข Physics Forums
January 3, 2016 - Data type of an array is char***. How to allocate memory for char*** data type? One string would be of type char *. An array of them would be of type char **. Why do you need three levels of indirection? Are you asking about a function parameter that is call by reference?
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Stack Overflow
stackoverflow.com โ€บ questions โ€บ 40450769 โ€บ char-memory-allocation
c - Char memory allocation - Stack Overflow
Connect and share knowledge within a single location that is structured and easy to search. Learn more about Teams ยท Get early access and see previews of new features. Learn more about Labs ... I am writing a program that reads a user input, but I don't want to give any upper limit to it's size, so I've decided to allocate it's memory dynamically like this: int main(int argc, char const *argv[]) { char ** INPUT; char * inputSize; int cl; printf("Enter your operation here: \n"); scanf("%s", INPUT); for(cl = 0; INPUT[cl] != '\0'; ++cl); inputSize = (char *) malloc((cl + 1) * sizeof(char)); return 0; }
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Quora
quora.com โ€บ How-do-I-dynamically-allocate-a-char-array-using-a-malloc-function-in-C
How to dynamically allocate a char array using a malloc function in C - Quora
In order to allocate memory dynamically using C language the following code will be enough: char *s = (char *)malloc(20 * sizeof(char)); The above line allocates memory for storing 20 characters or in fact 19 ch...
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1 of 2
10

Do like this:

char** list; 

list = malloc(sizeof(char*)*number_of_row);
for(i=0;i<number_of_row; i++) 
  list[i] = malloc(sizeof(char)*number_of_col);  

Additionally, if you are allocating memory dynamically. you are to free it as work done:

for(i=0;i<number_of_row; i++) 
  free(list[i] );
free(list);  

EDIT

In you revised question:

 int wordLine = 0, counter = 0, i;    

wordLine and counter are 0

before this code:

list = malloc(sizeof(char*)*wordLine+1);
for(i = 0;i < wordLine ; i++)
   list[i] = malloc(sizeof(char)*counter);  

you have to assign value to wordLine and counter variable

Also memory allocation should be before the following loop(outside):

 while((c = fgetc(myFile)) != EOF){
  :
  :
 }

EDIT:

New your third version of question. You are reading file two times. So you need to fseek(), rewind() to first char before second loop starts.

try with:

fseek(fp, 0, SEEK_SET); // same as rewind()
rewind(fp);             // same as fseek(fp, 0, SEEK_SET)

also I have doubt in your logic to calculate numberOfLines and maxNumberOfChars. please check that also

EDIT

I think your calculation for maxNumberOfChars = 0, numberOfLines = 0 is wrong try like this:

maxNumberOfChars = 0, numberOfLines = 0, numberOfChars = 0;
while((c = fgetc(myFile)) !=EOF){
     if(c == '\n'){
         numberOfLines++; 
         if(maxNumberOfChars < numberOfChars)
             maxNumberOfChars = numberOfChars;
         numberOfChars=0
     }
     numberOfChars++;
}    

maxNumberOfChars is max number of chars in a line.

Also change code:

malloc(sizeof(char)*(maxNumberOfChars + 1));  
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1

If I were you, I'd map the file to private memory, using mmap, and then iterate over the file, storing starts of words in an array of char** that you can increase as you go with realloc, and replacing line breaks with 0.

That way, you have your words in memory as a continuous block, you don't have to care about file I/O, because you have the entire text file in memory as char*, and you don't have to malloc an array of arrays.

For information on the functions, see the respective man pages, or drop me a comment :)

EDIT: If you don't know mmap yet, have a look at this: http://www.jimscode.ca/index.php/component/content/article/13-c/45-c-simple-mmap-example

Most C programmers today still try to read files into memory using fopen and friends, but that's completely unnecessary and introduces additionel levels of complexity. (buffering, growing arrays, ...) and mmap is a nice alternative that moves all the nasty work down to the OS

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Quora
quora.com โ€บ How-do-I-allocate-dynamically-memory-to-char**P
How to allocate dynamically memory to char**P - Quora
Answer (1 of 2): Double pointers are actually pointer to pointer. So we can say in anathor terms that they hold addresses for arrays. I.e. in your example p will be array in which each index will hold address of anathor character array. So the memory allocation goes like this. First allocate me...
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Wikibooks
en.wikibooks.org โ€บ wiki โ€บ A_Little_C_Primer โ€บ C_Dynamic_Memory_Allocation_&_Deallocation
A Little C Primer/C Dynamic Memory Allocation & Deallocation - Wikibooks, open books for an open world
September 10, 2008 - There may be no way of knowing how big an array needs to be for the specific task the program is performing, and so allocating an array in a fixed size will either result in wasted memory or in not having enough to do the job. The answer to this problem is to have the program allocate the memory at runtime, and that's what the "malloc()" library function does. For example, let's use "malloc()" to allocate an array of "char": /*malloc.c */ #include <stdio.h> #include <stdlib.h> /*For "malloc", "exit" functions.
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1 of 3
4

It is printing everything but it terminating ...

Consider your memory allocation statements:

char *a;
a=(char *)malloc(sizeof(char));

By allocating only sizeof(char) bytes to the buffer a, then attempting to write anything more than the null terminator to it, you are invoking undefined behavior. (Note: sizeof(char) in C is by definition equal to 1, always)

C strings are defined as a null terminated character array. You have allocated only one byte. The only legal C string possible is one containing only the null termination byte. But your code attempts to write much more, and in so doing encroaches on memory locations not owned by your process. So in general, when creating strings, follow two simple rules:

  • Determine max length of string you need
  • allocate memory to max length + 1 bytes to accommodate termination byte.

Example if max string is x characters long, create the memory for x + 1 characters:

char inputStr[] = {"This string is x char long"};
char string = malloc(strlen(inputStr) +1); //+1 for null byte
strcpy(string, inputStr);

Note, in C it is not recommended to cast the return of malloc() and family.

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1

You've two problems with your code. Firstly, you only allocate enough space for 1 character and since strings have to be NUL terminated, the longest string you could have is 0 characters long. Since you don't know how long the text you're going to read in, you could start with an arbitrary size (say 1024).

a=malloc(1024);

Secondly, scanf will only read up to the next space when you use "%s". It also isn't constrained by the available space in a. A better way to to read in an entire line of text, is to use fgets like this

fgets(a,1024,stdin);

This will read up to 1023 characters or up to and including the next newline character. It will NUL terminate the string for you as well.

You can then print it as a string.

printf("%s",a);
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Quora
quora.com โ€บ How-do-I-allocate-memory-for-char-*array-2-dynamically-in-C
How to allocate memory for char *array [] [2] dynamically in C - Quora
Answer (1 of 8): First of all, I dont like that empty brackets in first place. I understand what you want is 2 arrays of char pointers, so, it is better to redefine it as [code]char **array[2]; [/code]It can be used in the same way, but it is more clean. Now, each element of array will hold a ...
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Newtum
blog.newtum.com โ€บ c-data-types-memory-allocation-in-c-performance
C Data Types & Memory Allocation in C Performance
August 14, 2025 - Finally, it frees the allocated memory with `free` to prevent memory leaks. The `main()` function simply calls these two functions, bringing everything to life. This code nicely demonstrates handling both data types and memory management in C. Integer types: int: 10 short: 20 long: 30 Floating-point types: float: 10.500000 double: 20.500000 long double: 30.500000 Character type: char: A Dynamically allocated array: intArray[0]: 0 intArray[1]: 10 intArray[2]: 20 intArray[3]: 30 intArray[4]: 40
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Digipen
azrael.digipen.edu โ€บ ~mmead โ€บ www โ€บ Courses โ€บ CS120 โ€บ DynamicMemoryAllocation-1.html
Dynamic Memory Allocation
Note: The original version of malloc (from K&R C) returned a char * and so the returned pointed had to be cast to the correct type. Newer ANSI C compilers have malloc returning a void * pointer so the cast is not necessary in C. The cast is required in C++, however. You should never hard-code the size of the data types, since they may change. Do this instead: /* Proper memory allocation for 10 chars */ char *pc = (char *) malloc(10 * sizeof(char));