Learn The Null Terminator | Introduction to Strings in C

Definition

Definition: The null terminator ('\0') is a special character used in C to mark the end of a string. It signals to the program where the string data stops, allowing string-handling functions to work correctly.

When you work with strings in C, the null terminator is essential for safe and accurate string handling. The null terminator allows functions like printf, strlen, and many others to determine where the string ends. Without it, these functions would continue reading memory past the intended end of the string, potentially causing unpredictable results or program crashes. By marking the end of a string with '�', you ensure that only the intended characters are processed, and the program does not access memory it should not.

main.c


              1234567891011
            
#include <stdio.h>

int main() {
    char with_null[] = {'H', 'e', 'l', 'l', 'o', '\0'};
    char without_null[] = {'W', 'o', 'r', 'l', 'd'};

    printf("With null terminator: %s\n", with_null);
    printf("Without null terminator: %s\n", without_null);

    return 0;
}

In the output of this program, you will see that the string with the null terminator prints as expected: "Hello". However, the string without the null terminator may print extra, random characters after "World", or could even cause a crash. This happens because the printf function continues reading memory until it finds a \0, which is missing in the second array. As a result, the output is unpredictable and unsafe when the null terminator is not present.

main.c


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#include <stdio.h>

int main() {
    char manual[6];
    manual[0] = 'C';
    manual[1] = 'o';
    manual[2] = 'd';
    manual[3] = 'e';
    manual[4] = '!';
    manual[5] = '\0'; // Manually insert the null terminator

    printf("Manually terminated string: %s\n", manual);

    return 0;
}

Manually adding the '�' character is sometimes necessary when you build a string character by character, such as when reading input or constructing a string in a loop. If you forget to add the null terminator, the array will not be recognized as a proper string by C functions, leading to incorrect behavior or security risks. Always ensure the last character in your character array is '�' if you intend to use it as a string.

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Section 1. Chapter 2

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Definition

main.c


              1234567891011
            
#include <stdio.h>

int main() {
    char with_null[] = {'H', 'e', 'l', 'l', 'o', '\0'};
    char without_null[] = {'W', 'o', 'r', 'l', 'd'};

    printf("With null terminator: %s\n", with_null);
    printf("Without null terminator: %s\n", without_null);

    return 0;
}

main.c


              12345678910111213141516
            
#include <stdio.h>

int main() {
    char manual[6];
    manual[0] = 'C';
    manual[1] = 'o';
    manual[2] = 'd';
    manual[3] = 'e';
    manual[4] = '!';
    manual[5] = '\0'; // Manually insert the null terminator

    printf("Manually terminated string: %s\n", manual);

    return 0;
}

Everything was clear?

Thanks for your feedback!

Section 1. Chapter 2