Is there a function that copies all instances of a character into same indices in another string?

Question

Essentially what I'm looking for is a standard function that does something like this

void transcpy(char *target, const char *src, const char c)
{
    for (int i = 0; i < strlen(target)+1; i++)
        if (src[i] == c) target[i] = c;
}

this particular example assumes that target and src are the same length, but that's not a necessary precondition for what I'm looking for. Although c is assumed to appear in src.

e. g. transcpy(word, "word", 'r"); where word is "____" would mutate word to be "__r_"

this might just be specific to implementing a hangman game, but it seems like a useful enough function that it might have a standard implementation

Answer 1

I don't think there are a function in standard library that do that, I will implement this as:

char *replace_by_c(char *dest, const char *src, size_t size, char c) {
  for (size_t i = 0; i < size; i++) {
    if (src[i] == c) {
      dest[i] = c;
    }
  }
  return dest;
}

In C, it's common to let the user of a function handle the correct size.

char str_one[42];
char str_two[84];

size_t min = MIN(sizeof str_one, sizeof str_two);
replace_by_c(str_one, str_two, min, 'c');

This let a function to be use in a lot of situations, for example this function can work without NUL terminate and can handle a character NUL as c.

replace_by_c(dest, src, 42, '\0');