Return a string from function to main

问题

I want to return a string from a function (in the example funzione) to main. How to do this? Thank you!

#include <stdio.h>
#include <string.h>

#define SIZE (10)

/* TODO*/ funzione (void)
{
    char stringFUNC[SIZE];

    strcpy (stringFUNC, "Example");

    return /* TODO*/;
}

int main()
{
    char stringMAIN[SIZE];

    /* TODO*/

    return 0;
}

[EDITED] For those who need it, the complete version of the previous code (but without stringMAIN) is:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define SIZE (10)

char *funzione (void)
{
    char *stringa = malloc(SIZE);
    strcpy (stringa, "Example");

    return stringa;
} 

int main()
{
    char *ptr = funzione();

    printf ("%s\n", ptr);

    free (ptr);

    return 0;
}

回答1:

A string is a block of memory of variable length, and C cannot returns such objects (at least not without breaking compatibility with code that assumes strings cannot be returned)

You can return a pointer to a string, and in this case you have two options:

Option 1. Create the string dynamically within the function:

char *funzione (void)
{
    char *res = malloc (strlen("Example")+1);  /* or enough room to 
                                                  keep your string */
    strcpy (res, "Example");    
    return res;
}

In this case, the function that receives the resulting string is responsible for deallocate the memory used to build it. Failure to do so will lead to memory leaks in your program.

int main()
{
  char *str;

  str = funzione();
  /* do stuff with str */
  free (str);
  return 0;
}

Option 2. Create a static string inside your function and returns it.

char *funzione (void)
{
  static char str[MAXLENGTHNEEDED];

  strcpy (str, "Example");
  return str;
}

In this case you don't need to deallocate the string, but be aware that you won't be able to call this function from different threads in your program. This function is not thread-safe.

int main()
{
  char *str;

  str = funzione();
  /* do stuff with str */
  return 0;
}

Note that the object returned is a pointer to the string, so on both methods, the variable that receives the result from funzione() is not a char array, but a pointer to a char array.

回答2:

You can do this as

char *funzione (void)
{
    char *stringFUNC = malloc(SIZE);
    strcpy (stringFUNC, "Example");

    return stringFUNC;
}

In main, call it as

int main()
{
    char stringMAIN[SIZE];
    char *ptr = funzione ()
    ...

    free(ptr);
    return 0;
}

回答3:

#include <stdio.h>
#include <string.h>

#define SIZE 10

const char *funzione (void){
    const char *string = "Example";

    if(strlen(string) >= SIZE)
        return "";

    return string;
}

int main(void){
    char stringMAIN[SIZE];

    strcpy(stringMAIN, funzione());

    printf("%s", stringMAIN);

    return 0;
}

来源：https://stackoverflow.com/questions/21068790/return-a-string-from-function-to-main

标签

string

function

main