C function to Swap strings

In C programming, swapping strings involves exchanging the contents of two string variables. This can be achieved through character-by-character swapping or by swapping string pointers.

Syntax

// Character-by-character swapping
void swapStrings(char str1[], char str2[]);

// Pointer swapping
void swapPointers(char **str1, char **str2);

Method 1: Character-by-Character Swapping

This method swaps each character of the strings individually −

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

int main() {
    char st1[] = "My 1st string";
    char st2[] = "My 2nd string";
    char swap;
    int i = 0;
    
    printf("Before swapping:<br>");
    printf("st1: %s<br>", st1);
    printf("st2: %s<br>", st2);
    
    // Find the maximum length to ensure complete swap
    int len1 = strlen(st1);
    int len2 = strlen(st2);
    int maxLen = (len1 > len2) ? len1 : len2;
    
    // Swap characters
    for(i = 0; i < maxLen; i++) {
        swap = st1[i];
        st1[i] = st2[i];
        st2[i] = swap;
    }
    
    printf("\nAfter swapping:<br>");
    printf("st1: %s<br>", st1);
    printf("st2: %s<br>", st2);
    
    return 0;
}

Before swapping:
st1: My 1st string
st2: My 2nd string

After swapping:
st1: My 2nd string
st2: My 1st string

Method 2: Using Temporary String

This approach uses a temporary array to store one string during the swap −

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

int main() {
    char str1[] = "Hello";
    char str2[] = "World";
    char temp[100];
    
    printf("Before swapping:<br>");
    printf("str1: %s<br>", str1);
    printf("str2: %s<br>", str2);
    
    // Copy str1 to temp, str2 to str1, temp to str2
    strcpy(temp, str1);
    strcpy(str1, str2);
    strcpy(str2, temp);
    
    printf("\nAfter swapping:<br>");
    printf("str1: %s<br>", str1);
    printf("str2: %s<br>", str2);
    
    return 0;
}

Before swapping:
str1: Hello
str2: World

After swapping:
str1: World
str2: Hello

Key Points

• Character-by-character method works in-place but requires strings of similar length for complete swap.
• Temporary string method is safer and handles strings of different lengths correctly.
• Always ensure sufficient buffer size when using strcpy() to avoid buffer overflow.

Conclusion

String swapping in C can be accomplished through character swapping or using temporary storage. The strcpy() approach is generally preferred as it handles strings of different lengths safely.