Question

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What is the function to replace string in C?

I am trying to replace a certain character in my string with multiple characters. Here is an example of what I am trying to do.

Say I have the string “aaabaa”

I want to replace all occurrences of the character “b” with 5 “c”s.

So when I am done, “aaabaa” becomes “aaacccccaa”

I have written the following code:

#include <stdio.h>
#include <string.h>
int main(void)
{
    char s[20] = "aaabaa";
    int i, j;
    for (i=0; s[i]!= '\0'; i++)
    {
        if (s[i] == 'b')
        {
            for (j=0; j<5; j++)
            {
                s[i+j] = 'c';
            }
        }
    }
    printf("%s\n", s);
}

My output from this function is “aaaccccc”. It appears that it just overwrites the last two a’s with the c’s. Is there any way I would have it so that these last couple of a’s dont get overwritten?

Answer 1

Your problem is that you replace the “ccccc” into the original string thus overwriting the remaining characters after what you wish to replace… You should copy into a new string and keep track of two indices – one in each.

And be happy that you declared char s[20] larger than the size of your original string plus the replace values, as otherwise you’d have created a buffer overflow vulnerability in your critical login system 🙂

Cheers,