C结构字段分配覆盖另一个字段

Question

为了好玩，我正在编写一个梦幻足球选秀程序。

我遇到了一个奇怪的问题。我为 struct 字段分配了一个值，这发生了，但它也将该值分配给了 struct 中的另一个字段。为困惑的调试 printf 语句道歉。

我显然对 struct 字段赋值有些不理解。

代码:

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

#define TRUE 1

int QB_count = 0;
int RB_count = 0;
int WR_count = 0;
int TE_count = 0; 
int DEF_count = 0;

struct Player { 
    char *name;
    char *position;
    int age;
    int bye_week;
};

int get_name (struct Player *drafted) {
    char name[20];
    fputs("Enter Player Name: ", stdout);
    fflush(stdout);
    if (fgets(name, sizeof name, stdin) != NULL){
        char *newline = strchr(name, '\n');
        if (newline != NULL){
            *newline = '\0';
        }
        drafted->name = name;
        printf("You've drafted: %s\n", drafted->name);
    }
    return 0;
}

int get_position(struct Player *drafted){
    char position[20];
    int depth;
    char *nametemp = drafted->name;
    printf("nametemp: %s\n", nametemp);
    fputs("Enter Player Position in 'QB/RB/WR/TE/DEF' format: ", stdout);
        fflush(stdout);
        if (fgets(position, sizeof position, stdin) != NULL){
                char *newline = strchr(position, '\n');
                if (newline != NULL){
                        *newline = '\0';
                }
                drafted->position = position;

        if (strcmp(position, "QB") == 0){
            QB_count++;
            depth = QB_count;

        } else if (strcmp(position, "RB") == 0){
                        RB_count++;
                        depth = RB_count;

                } else if (strcmp(position, "WR") == 0){
                WR_count++;
                        depth = WR_count;

                } else if (strcmp(position, "TE") == 0){
                        TE_count++;
                        depth = TE_count;

                } else if (strcmp(position, "DEF") == 0){
                        DEF_count++;
                        depth = DEF_count;

                } else {
            printf("Please re-enter position information using the format 'QB' or 'qb'\n");
            get_position(drafted);
            return 0;
        }
        drafted->name = nametemp;
        printf("NAME: %s\n", drafted->name);
        printf("You've drafted %s at: %s%d\n", drafted->name, drafted->position, depth);
        }
        return 0;

}

int get_age (struct Player *drafted){
    return 0;
}

int get_bye_week (struct Player *drafted){
    return 0;
}

int main (){ 
    int stop = 0;
    char text[20];
    while (TRUE){
        struct Player drafted;
        printf("Welcome to the 2012 Draft Day Program\n");
        get_name (&drafted);
        printf("NAME_MAIN: %s\n", drafted.name);
        get_position(&drafted);
        printf("You've drafted %s at: %s\n", drafted.name, drafted.position);
        get_age(&drafted);
        get_bye_week(&drafted);
        fputs("Would you like to draft another player?\n" 
            "Enter '1' for no, '0' for yes\n", stdout);
        fflush(stdout);
        if(fgets(text, sizeof text, stdin)){
            int number;
            if (sscanf(text, "%d", &number) == 1){
                if (number == 1){
                    printf("Draft Ended!\n");
                    break;
                }       
            }
        }
    }
    return 0;
}

结果输出是:

Welcome to the 2012 Draft Day Program
Enter Player Name: Aaron Rodgers
You've drafted: Aaron Rodgers
NAME_MAIN: Aaron Rodgers
nametemp: Aaron Rodgers
Enter Player Position in 'QB/RB/WR/TE/DEF' format: QB
NAME: QB
You've drafted QB at: QB1
You've drafted QB at: QB
Would you like to draft another player?
Enter '1' for no, '0' for yes
1
Draft Ended!

为什么 drafted.name 变成了“QB”？

Answer 1

在您的 get_name 函数中，您将分配给 struct Player 的 name 字段一个堆栈变量 name.

在这一行中:

drafted->name = name;

name 是在函数中声明的，因此它的范围 仅限于该函数。一旦 get_name 返回，变量就会超出范围，并尝试使用该内存调用未定义的行为。

不是使用简单赋值，而是需要使用malloc为drafted->name分配空间，并使用strncpy做一个名称的副本。如果 strdup 可用，您可以使用它来分配空间并一步完成复制。或者，您可以在读取名称之前为 drafted->name 分配空间，并用它代替 name 变量。

作为最后一个选项，如果您假设名称的最大长度 - 您当前的代码允许名称的字符串长度最大为 19 - 您可以简单地为每个 声明一个该大小的数组>结构播放器:

struct Player
{ 
    char name[NAME_MAXLEN];

get_position 函数中的 position 字段也有同样的问题。