Lære Concatenating Strings | String Manipulation Functions

Definition

Definition:
The strcat function in C joins (concatenates) two strings by appending the source string to the end of the destination string. The strncat function works similarly, but allows you to specify the maximum number of characters to append from the source, helping prevent buffer overflows.

Concatenation is the process of joining two or more strings end to end. In C, concatenation is not performed with a simple operator; instead, you use specific functions such as strcat and strncat. When you concatenate, the content of the source string is copied to the end of the destination string, starting at the null terminator (\0) of the destination.

It is crucial to ensure that the destination array has enough space to hold both the original contents and the new data being appended. If the buffer is too small, you risk overwriting memory, which can cause unpredictable behavior or security issues.

main.c


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

int main() {
    char dest[50] = "Hello, ";
    char src[] = "world!";

    strcat(dest, src);

    printf("Concatenated string: %s\n", dest);
    return 0;
}

Using strcat is straightforward, but it is also risky. If the destination buffer is not large enough to hold the combined string and the null terminator, strcat will write past the end of the array. This can lead to buffer overflow, which may corrupt data or open your program to security vulnerabilities.

main.c


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

int main() {
    char dest[12] = "Hello, ";
    char src[] = "world!";

    strncat(dest, src, sizeof(dest) - strlen(dest) - 1);

    printf("Safely concatenated string: %s\n", dest);
    return 0;
}

The strncat function helps prevent buffer overflow by letting you specify the maximum number of characters to append. By calculating the remaining space in the destination buffer and passing it to strncat, you ensure that the resulting string will not exceed the buffer size, and the null terminator will always be in place.

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Definition

main.c


              12345678910111213
            
#include <stdio.h>
#include <string.h>

int main() {
    char dest[50] = "Hello, ";
    char src[] = "world!";

    strcat(dest, src);

    printf("Concatenated string: %s\n", dest);
    return 0;
}

main.c


              12345678910111213
            
#include <stdio.h>
#include <string.h>

int main() {
    char dest[12] = "Hello, ";
    char src[] = "world!";

    strncat(dest, src, sizeof(dest) - strlen(dest) - 1);

    printf("Safely concatenated string: %s\n", dest);
    return 0;
}

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Tak for dine kommentarer!

Sektion 3. Kapitel 2