C strings are one-dimensional arrays of characters terminated by a null character (\0). Unlike higher-level languages, C does not have a built-in string data type; instead, strings are implemented as arrays of char with a \0 at the end to mark the string's termination.
Key Characteristics:
Null-terminated: The
\0character is essential; without it, string functions may behave unpredictably.Declared using
char: Strings are declared withcharfollowed by the name and square brackets, e.g.,char str[].Initialized in multiple ways:
Using a string literal:
char str[] = "Hello";(compiler adds\0automatically).Character-by-character:
char str[] = {'H', 'e', 'l', 'l', 'o', '\0'};.
Common Operations:
Printing: Use
printf("%s", str);to print a string.Input: Use
scanf("%s", str)(stops at whitespace) orfgets(str, size, stdin)(reads entire line, including spaces).Length: Use
strlen(str)from<string.h>to get the length (excludes\0).Copying/Comparing: Use
strcpy,strcat,strcmp, etc., from<string.h>.
Note: Always ensure the destination array is large enough to hold the string and the null terminator to prevent buffer overflows.
C does not and never has had a native string type. By convention, the language uses arrays of char terminated with a null char, i.e., with '\0'. Functions and macros in the language's standard libraries provide support for the null-terminated character arrays, e.g., strlen iterates over an array of char until it encounters a '\0' character and strcpy copies from the source string until it encounters a '\0'.
The use of null-terminated strings in C reflects the fact that C was intended to be only a little more high-level than assembly language. Zero-terminated strings were already directly supported at that time in assembly language for the PDP-10 and PDP-11.
It is worth noting that this property of C strings leads to quite a few nasty buffer overrun bugs, including serious security flaws. For example, if you forget to null-terminate a character string passed as the source argument to strcpy, the function will keep copying sequential bytes from whatever happens to be in memory past the end of the source string until it happens to encounter a 0, potentially overwriting whatever valuable information follows the destination string's location in memory.
In your code example, the string literal "Hello, world!" will be compiled into a 14-byte long array of char. The first 13 bytes will hold the letters, comma, space, and exclamation mark and the final byte will hold the null-terminator character '\0', automatically added for you by the compiler. If you were to access the array's last element, you would find it equal to 0. E.g.:
const char foo[] = "Hello, world!";
assert(foo[12] == '!');
assert(foo[13] == '\0');
However, in your example, message is only 10 bytes long. strcpy is going to write all 14 bytes, including the null-terminator, into memory starting at the address of message. The first 10 bytes will be written into the memory allocated on the stack for message and the remaining four bytes will simply be written on to the end of the stack. The consequence of writing those four extra bytes onto the stack is hard to predict in this case (in this simple example, it might not hurt a thing), but in real-world code it usually leads to corrupted data or memory access violation errors.
Does C have a string type? - Stack Overflow
What is a literal string & char array in C? - Stack Overflow
New to C. If C does not have strings, then what exactly is printf doing?
Nylon strings to play in Drop C
How to reverse a string in C?
How to copy one string in C to another?
How to input a C string with spaces?
My friends are spilt down the middle on this. Half of us think since a c doesn’t have built in strings and only arrays of characters that they don’t. While the other half think that the array of characters would be considered string.
C does not and never has had a native string type. By convention, the language uses arrays of char terminated with a null char, i.e., with '\0'. Functions and macros in the language's standard libraries provide support for the null-terminated character arrays, e.g., strlen iterates over an array of char until it encounters a '\0' character and strcpy copies from the source string until it encounters a '\0'.
The use of null-terminated strings in C reflects the fact that C was intended to be only a little more high-level than assembly language. Zero-terminated strings were already directly supported at that time in assembly language for the PDP-10 and PDP-11.
It is worth noting that this property of C strings leads to quite a few nasty buffer overrun bugs, including serious security flaws. For example, if you forget to null-terminate a character string passed as the source argument to strcpy, the function will keep copying sequential bytes from whatever happens to be in memory past the end of the source string until it happens to encounter a 0, potentially overwriting whatever valuable information follows the destination string's location in memory.
In your code example, the string literal "Hello, world!" will be compiled into a 14-byte long array of char. The first 13 bytes will hold the letters, comma, space, and exclamation mark and the final byte will hold the null-terminator character '\0', automatically added for you by the compiler. If you were to access the array's last element, you would find it equal to 0. E.g.:
const char foo[] = "Hello, world!";
assert(foo[12] == '!');
assert(foo[13] == '\0');
However, in your example, message is only 10 bytes long. strcpy is going to write all 14 bytes, including the null-terminator, into memory starting at the address of message. The first 10 bytes will be written into the memory allocated on the stack for message and the remaining four bytes will simply be written on to the end of the stack. The consequence of writing those four extra bytes onto the stack is hard to predict in this case (in this simple example, it might not hurt a thing), but in real-world code it usually leads to corrupted data or memory access violation errors.
To note it in the languages you mentioned:
Java:
String str = new String("Hello");
Python:
str = "Hello"
Both Java and Python have the concept of a "string", C does not have the concept of a "string". C has character arrays which can come in "read only" or manipulatable.
C:
char * str = "Hello"; // the string "Hello\0" is pointed to by the character pointer
// str. This "string" can not be modified (read only)
or
char str[] = "Hello"; // the characters: 'H''e''l''l''o''\0' have been copied to the
// array str. You can change them via: str[x] = 't'
A character array is a sequence of contiguous characters with a unique sentinel character at the end (normally a NULL terminator '\0'). Note that the sentinel character is auto-magically appended for you in the cases above.
A string literal is an unnamed string constant in the source code. E.g. "abc" is a string literal.
If you do something like char str[] = "abc";, then you could say that str is initialized with a literal. str itself is not a literal, since it's not unnamed.
A string (or C-string, rather) is a contiguous sequence of bytes, terminated with a null byte.
A char array is not necessarily a C-string, since it might lack a terminating null byte.
What is a literal string & char array in C?
C has 2 kinds of literals: string literals and compound literals. Both are unnamed and both can have their address taken. string literals can have more than 1 null character in them.
In the C library, a string is characters up to and including the first null character. So a string always has one and only one null character, else it is not a string. A string may be char, signed char, unsigned char.
Copy// v---v string literal 6 char long
char *s1 = "hello";
char *s2 = "hello\0world";
// ^----------^ string literal 12 char long
char **s3 = &"hello"; // valid
// v------------v compound literal
int *p1 = (int []){2, 4};
int **p2 = &(int []){2, 4}; // vlaid
C specifies the following as constants, not literals, like 123, 'x' and 456.7. These constants can not have their address taken.
Copyint *p3 = &7; // not valid
C++ and C differ in many of these regards.
A chararray is an array of char. An array may consist of many null characters.
Copychar a1[3]; // `a1` is a char array size 3
char a2[3] = "123"; // `a2` is a char array size 3 with 0 null characters
char a3[4] = "456"; // `a3` is a char array size 4
char a4[] = "789"; // `a4` is a char array size 4
char a5[4] = { 0 }; // `a5` is a char array size 4, all null characters
The following t* are not char arrays, but pointers to char.
Copychar *t1;
char *t2 = "123";
int *t3 = (char){'x'};
Brand new to C, and I am told that there is no string data type. So I am just curious, if that id the case, then how exactly is something like: printf(“Hello World”) a thing?