Question

I have the following function which gets called multiple times in my code:

char* get_section_name(const char* section, const char* value) {

  char *tmp = (char *)malloc(STR_LEN * sizeof(char));

  if(strlen(section)>0) {

      strcat(tmp, section);

      strcat(tmp,".");

  }

  strcat(tmp, value);    

  return tmp;

}

and I call it in other functions like this:

section_name = get_section_name(data->model_name,"params_default");

What is the best way to free this memory? Can I just call free(section_name) when I am done?

Answer 1

Yes free, however, you could consider a different name that makes it clear it is allocating memory. Also, you could make use of sprintf for combining 2 strings and strdup for just copying one.

char* create_section_name(const char* section, const char* value) { 
  const int sectionLen = strlen(section);   

  if(sectionLen>0) {
      //+1 for the period and +1 for the null
      char *tmp = (char *)malloc((sectionLen + strlen(value) + 2) * sizeof(char));
      //do that often? consider a newString(size) macro. See below
      sprintf(tmp, "%s.%s", section, value);    
      return tmp;
  }
  else {    
    return strdup(value);
  }
}

This assumes you don’t need the full STR_LEN, it uses just enough in both cases.

newString macro I suggested:

#define newString(size) (malloc((size) * sizeof(char)))

Or it can even automatically add one for the null:

#define newString(size) (malloc(((size)+1) * sizeof(char)))

Then malloc is replaced with this:

char *tmp = newString(sectionLen + strlen(value) + 1); //+1 for period