从C函数返回的字符串是垃圾

Question

i've been working on a RPG in C language lately, and i've come accross some difficulties for saving / loading some datas from a text file.

Here is the (simplified to make it short) code :

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

struct player{
    int id;
    char* name;
};

void save(struct player* player)
{
    FILE* fp = 0;
    char* buffer = 0;

    fp = fopen("./gamesave.txt", "w");
    fclose(fp);
    buffer = malloc(80);
    memset(buffer, 0, 80);

    snprintf( buffer, 80, "%d|%s|\n", player->id, player->name);
    fp = fopen("./gamesave.txt", "a");
    fputs(buffer, fp);
    free(buffer);
    fclose(fp);
}

struct player* load()
{
    FILE* fp = 0;
    char* buffer = 0;
    struct player* player = malloc(sizeof(struct player));
    char tokens[] = "|\n";

    buffer = malloc (80);
    memset(buffer, 0, 80);

    fp = fopen("./gamesave.txt", "r");

    if (fgets(buffer, 80, fp)) {
        char temp[20];
        player->id = atoi(strtok(buffer, tokens));
        strcpy(temp, strtok(NULL, tokens));
        player->name = temp;
        printf("during load : name is %s\n", player->name);
    }
    fclose(fp);
    free(buffer);
    return player;
}

void main()
{


    struct player* player = malloc(sizeof(struct player));
    player->id = 5;
    player->name = "Bobby";
    printf("before save : my name is %s and id is %d\n", player->name, player->id);

    save(player);
    struct player* playerN = load();
    printf("after load : name is %s and id is %d", playerN->name, playerN->id);
}

This is my latest try in doing this but i've tried many differents ways of doing it, but it almost always ends in the same problem : i can't seem to get the right values for strings although it works for integers.I can print the name of the player before save, during the load function, but after the load it just prints garbage (the id works just fine).

My guess is that it has to do with some kind of memory problem but that's it, couldn't solve it after hours and hours.

Thanks in advance.

Answer 1

You need to allocate space for player->name .

You are using automatic variable temp for this, and its lifetime ends when the function returns. Auto variables are on the stack.

So you are taking an address on the stack and keeping it as your object. This leaks a pointer to your current stack level because you return it. It's OK to use pointers to automatic variables, but only while that function instance is active, ie, in it's life cycle and in functions it calls.