This does not happen by magic. You have in your code:
for (i = 0; i <= strlen(line); i++)
^^
The loop index i runs till strlen(line) and at this index there is a nul character in the character array and this gets copied as well. As a result your end result has nul character at the desired index.
If you had
for (i = 0; i < strlen(line); i++)
^^
then you had to put the nul character manually as:
for (i = 0; i < strlen(line); i++)
{
if ( line[i] != ' ' )
{
non_spaced[j] = line[i];
j++;
}
}
// put nul character
line[j] = 0;
Top answer 1 of 7
13
This does not happen by magic. You have in your code:
for (i = 0; i <= strlen(line); i++)
^^
The loop index i runs till strlen(line) and at this index there is a nul character in the character array and this gets copied as well. As a result your end result has nul character at the desired index.
If you had
for (i = 0; i < strlen(line); i++)
^^
then you had to put the nul character manually as:
for (i = 0; i < strlen(line); i++)
{
if ( line[i] != ' ' )
{
non_spaced[j] = line[i];
j++;
}
}
// put nul character
line[j] = 0;
2 of 7
8
Others have answered your question already, but here is a faster, and perhaps clearer version of the same code:
void line_remove_spaces (char* line)
{
char* non_spaced = line;
while(*line != '\0')
{
if(*line != ' ')
{
*non_spaced = *line;
non_spaced++;
}
line++;
}
*non_spaced = '\0';
}
TutorialsPoint
tutorialspoint.com › cprogramming › c_strings.htm
Strings in C
A string in C is a one-dimensional array of char type, with the last character in the array being a "null character" represented by '\0'. Thus, a string in C can be defined as a null-terminated sequence of char type values.
Videos
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GeeksforGeeks
geeksforgeeks.org › c language › strings-in-c
Strings in C - GeeksforGeeks
2 weeks ago - A string in C is an array of characters terminated by a null character '\0'. The null character '\0' marks the end of the string.
Reddit
reddit.com › r/cpp_questions › why are null terminators needed to signify the end of a string when arrays don’t have anything to signify the end of it?
r/cpp_questions on Reddit: Why are null terminators needed to signify the end of a string when arrays don’t have anything to signify the end of it?
August 19, 2023 -
All strings inherently have ‘\0’ at the end to know when the end of the string is.
However, arrays don’t have anything like this. You can keep accessing indexes to infinity and it’ll output something.
So I’m wondering, exactly why are null terminators needed in strings if nothing similar like is applied to c++ arrays?
What’s the benefit?
TLDR: why are null terminators needed in strings but there’s nothing to signify the end of an array?
Top answer 1 of 13
35
All strings inherently have ‘\0’ at the end to know when the end of the string is. Notably its just a convention. 60 years ago the C language decided that arrays should not be first class constructs in the language. That is why raw arrays decay into pointers and you have to manually pass around their size (at least in C, in C++ you can capture it as a template parameter). However you didnt want to pass around the size of a string all the time. As a result using a null terminator for character strings was a "good" choice. Essentially they didnt want to treat arrays as objects, but wanted to use character arrays as objects. All C-strings and std::string (which wants to be usable with C interfaces) have this. However, a std::string_view can view a character array without a null terminator - because it internally stores the size/end. However, arrays don’t have anything like this. You can keep accessing indexes to infinity and it’ll output something. No you cant. Accessing an array out of bounds is undefined behaviour. Formally, you cannot reason about it. It may "appear to work" (since the produced assembly will just do a simple index calculation). However, if the memory you are trying to access doesnt belong to your program, the OS will terminate your program with a segfault. If you write out of bounds, you may trash your stack, or you may also get a segfault. there’s nothing to signify the end of an array? Another important point here is the type. With characters, we can easily chose a non-printable, special value as the sentinel value to signal the end. But what could that sentinel value be for e.g. int. 0? Surely not. We want to be able to store zeros in our arrays. INT_MAX? But what if I actually want to store that value? Essentially there is no possible sentinal value. This becomes even more obvious when the type isnt fundamental.
2 of 13
9
std::string doesn't actually use the NULL terminator. It contains its length as a typical member variable. However, it does ensure its underlying data is NULL terminated for compatibility with i.e C-style APIs via c_str(). And... if I provided you a library using std::string as parameters, your C++ std::string (from i.e MSVC) might have a different size / layout to my std::string (from i.e MINGW). C++ does not traditionally have a stable binary ABI. Instead by extracting and passing around the raw NULL terminated char*, we can sidestep this. This is why many C++ libraries take in raw C-style strings.
Reddit
reddit.com › r/learnprogramming › doubt in strings in c
r/learnprogramming on Reddit: Doubt in Strings in C
July 8, 2024 -
Stupid Doubt maybe but, still one that makes me wanna rage quit it, can someone please tell me why is there a null character at the end of a string, but not at the end of a usual integer array? like why is a char array special and needs a char to let it know of the end of it. or why the usual array is smarter in knowing where it ends. Thanks in advance
Top answer 1 of 5
85
What makes you think that usual array knows where it ends?
2 of 5
35
Char array is just a block of memory to store bytes, nothing forces you to end it up with a null char. It just makes it easier to work with strings that way. In the other hand an int array is a block of memory to store a group of bytes, so no null terminated. Edit: just wanted to clarify, no array in C knows where it ends, they are just pointers to memory blocks, there is nothing special about an int array, you still need to save the length on another variable so you can work with it.
Eskimo
eskimo.com › ~scs › cclass › notes › sx8.html
Chapter 8: Strings
Strings in C are represented by arrays of characters. The end of the string is marked with a special character, the null character, which is simply the character with the value 0. (The null character has no relation except in name to the null pointer. In the ASCII character set, the null character ...
Weber State University
icarus.cs.weber.edu › ~dab › cs1410 › textbook › 8.Strings › c_string.html
8.2. C-Strings
C-Strings are character arrays with one additional feature: they mark the end of the string text with a special character called the null termination character. The null termination character or null terminator is the character equivalent of zero, which C++ denotes with the escape sequence ...
Cprogramming
cboard.cprogramming.com › c-programming › 108449-check-end-string.html
check end of string
October 23, 2008 - You can use strrchr(a, '\n') to locate the the last occurence of a newline in the string that's stored in the array but strchr(a, '\n') ought to do the job because the standard C lib ensures that each line is terminated by a newline so there can't be multiple occurrences of the newline character ...
Reddit
reddit.com › r/c_programming › why is a null character at the end of a string important
r/C_Programming on Reddit: Why is a null character at the end of a string important
March 30, 2023 -
I get that it marks the end of the string, but if I have the size with me when I declared the string what is the use of it. Plus if it’s so important why don’t int arrays have a null char at the end. The only reason I can think of is to output it into the terminal without going over the limit but I’m not sure if that’s the only reason or if it’s even a right reason
Top answer 1 of 5
6
What do you mean you "declared the string." C has no string type, just arrays of characters. Unfortunately, unless you retain the size of the array somewhere, you won't know where the end is unless you put a null there. Note that arrays are only half-assed types in C. You can't assign them, and when they appear in function declarations the compiler silently replaces them with pointers to their first member. Essentially, every language in the world does strings one of two ways, either it puts some sentinal value (like a null) at the end or it explicitly stores the length somewhere.
2 of 5
3
Many string functions in the stdlib require them. Because... All arrays (including strings) passed to functions, decay to a pointer to the first element of the array. For these (and your own) it will need to know where the string ends. And... Without it, it's a just an array of characters.
Wikipedia
en.wikipedia.org › wiki › Null-terminated_string
Null-terminated string - Wikipedia
March 25, 2025 - In computer programming, a null-terminated string is a character string stored as an array containing the characters and terminated with a null character (a character with an internal value of zero, called "NUL" in this article, not same as the glyph zero). Alternative names are C string, which ...
W3Schools
w3schools.com › c › c_strings.php
C Strings
This is known as the "null terminating character", and must be included when creating strings using this method. It tells C that this is the end of the string.
Reddit
reddit.com › r/c_programming › passing a pointer to indicate the end of a string?
r/C_Programming on Reddit: Passing a pointer to indicate the end of a string?
March 29, 2016 -
Strings are correctly passed to printf() as a char * to the first character of the string. Normally, printf() goes until it finds a null byte. Is there a way to supersede that normal search for the null byte, and feed a pointer to the last character in printf?
Top answer 1 of 5
7
Do some pointer math. Let's visualize it: Pos: 0123456 Str: Hello! Ptr: ^- Pointer The length of this string is 6 characters. So if we add 6 to the pointer, then the pointer points to the terminating character (\0): Pos: 0123456 Str: Hello! Ptr: ^- Pointer Off by one! So we just fix it by subtracting it by one, so it points to the last character in the string: 0123456 Hello! ^- Pointer So the formular is str + str_len - 1, where str is the pointer to the string and str_len is the length of the string. Let's test it with some code: #include #include int main() { char str[] = "Hello!"; printf("Normal: %s\n", str); printf("Last: %s\n", str + strlen(str) - 1); return 0; } Output: Normal: Hello! Last: ! Yep, it works!
2 of 5
5
The way strtok_r works is that it replaces the delimeter with a NULL byte, and stores the original end of the string in **saveptr. The man page tells you exactly this. It's up to you to implement it the same way - if the first argument is NULL and saveptr is not, then you know to continue where you left off.
Quora
quora.com › Why-does-a-string-in-C-end-with-0-but-not-in-arrays-What-is-the-reason-for-that
Why does a string in C end with '/0' but not in arrays? What is the reason for that? - Quora
Answer: There are many different reasons behind it When you end a array of string you need to add /0 because by this only the library knows where the string ends. And with the end of string knowledge you can perform certain actions on that string ...
Sololearn
sololearn.com › en › Discuss › 1207298 › when-should-i-put-a-0-to-the-end-of-a-string-or-character-array
When should I put a '\0' to the end of a string or character array? | Sololearn: Learn to code for FREE!
April 10, 2018 - Historical value: In the older days, 0 was all a C function had to tell it had reached the end (preventing overflow) of a string without a user-supplied length. strlen is a good example here: Arrays of char are passed by reference and strlen counts from the start address until it encounters a zero.
Cplusplus
cplusplus.com › reference › string › string › end
std::string::end
Returns an iterator pointing to the past-the-end character of the string. The past-the-end character is a theoretical character that would follow the last character in the string. It shall not be dereferenced.
Cppreference
en.cppreference.com › w › cpp › string › basic_string › end
std::basic_string<CharT,Traits,Allocator>::end, std::basic_string<CharT,Traits,Allocator>::cend - cppreference.com
Returns an iterator to the character following the last character of the string. This character acts as a placeholder, attempting to access it results in undefined behavior. ... Iterator to the character following the last character. ... #include <algorithm> #include <iostream> #include <iterator> ...
University of Texas
farside.ph.utexas.edu › teaching › 329 › lectures › node21.html
Character strings
Here, 'f' represents the character ``f'', etc., and '\0' represents the so-called null character (ASCII code 0), which is used in C to signal the termination of a character string. The null character is automatically added to the end of any character string enclosed in double quotes.
GitHub
github.com › portfoliocourses › c-example-code › blob › main › endswith.c
c-example-code/endswith.c at main · portfoliocourses/c-example-code
if (end_length > string_length) return false; · // check the characters at the end of string to see if any of them do no match · // the characters in the end string, if any do no not, the string does not · // end with the end string, and we can return false ·
Author portfoliocourses
Learn C
learnc.net › home › learn c programming › c string
C String
April 13, 2025 - Therefore, a string in C is an array of characters. To mark the end of a string, C uses a special character '\0'. The '\0' is called the null character.
GeeksforGeeks
geeksforgeeks.org › c language › string-functions-in-c
C String Functions - GeeksforGeeks
July 26, 2025 - C language provides various built-in functions that can be used for various operations and manipulations on strings. These string functions make it easier to perform tasks such as string copy, concatenation, comparison, length, etc. The <string.h> header file contains these string functions. The strlen() function is used to find the length of a string.