An example C buffer implementation

example_buffer.c

int convert_blank_to_quote(const char* source, char* dest, int64_t buffer_size)
{
  --buffer_size; // the last character would be '\0'
  if (buffer_size <= 0) {
    return -1; // illegal argument: buffer size too small
  }

  int64_t i = 0;
  for (const char* p = source; *p != '\0' && i < buffer_size; ++p, ++i) {
    *(dest + i) = p == ' ' ? '@' : *p;
  }
  *(dest + buffer_size) = '\0';

  return buffer_size;
}