void api_func(int input_int, char* input_string, int* output_int, char** output_string);

void foo()
{
  int a;
  char b[] = "Abanamat"; 
  int res; 
  char* comment;
  
  api_func( a, b, &res, &comment);
}

void api_func(int input_int, char* input_string, int* output_int, char** output_string)
{

  // read the input
  int a = input_int;
  char *buf[2048];
  strncpy(buf,input_string,2048);
  
  // ...

  // produce the output
  *output_int = a + 42;
  *output_string = malloc( (strlen(buf)+1)*sizeof(char) );
  strcpy(*output_string,buf);
}