Question

I needed a function to return a string. I used the following code to declare the function:

const char* serv_con(char app_data[50])
{
    char send_data[1024],recv_data[1024];
    //i am avoiding code segments irrelevant to the issue.
    return recv_data;
}

and then called the function in the main like this:

int main()
{
    char ser_data[50], app_data[50];
    ser_data[0] = '\0';
    app_data[0] = '\0';
    //avoiding code segments irrelevant to the issue.
    app_data = serv_con(ser_data); //function call
}

On compiling it gives the error:

connect.c:109: error: incompatible types when assigning to type ‘char[50]’ from type ‘const char *’

Then i replaced the const char in the declaration with std::string. The declaration now is as follows:

std::string serv_con(char app_data[50])
{
    char send_data[1024],recv_data[1024];
    //avoiding code segments irrelevant to the issue.
    return recv_data;
}

And called it in the same way as mentioned above. But still it gives the following error on compiling:

connect.c:13: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘:’ token

Please tell me how I can give a string as a return type from a function. The platform I work on is linux. Thanks in advance.

Answer 1

const char* serv_con(char app_data[50])
{
  char send_data[1024],recv_data[1024];
  //i am avoiding code segments irrelevant to the issue.
  return recv_data;
}

this cannot work, since you’re returning a pointer to a local variable, which is invalid after returning. You need to allocate recv_data on the heap in order to use it after returning

char* serv_con(char app_data[50])
{
  char send_data[1024];
  char *recv_data = malloc(1024);
  if (!recv_data)
      return NULL;

  // ...
  return recv_data;
 }

then change the main function to be something like

int main()
{
 char ser_data[50];
 char *app_data;
 ser_data[0] = '\0';
 //avoiding code segments irrelevant to the issue.
 app_data = serv_con(ser_data); //function call
 if (!app_data) {
   // error
 }
}