c - Malloc 和总线 10 运行时错误帮助 C

Question

因此，我正在处理一项特定的编程作业，我认为该作业需要使用我不熟悉的 malloc() 函数。我的理解是，如果您使用 malloc() ，则必须在使用完内存后释放内存，否则最终可能会出现奇怪的行为。我想知道这是否就是我每隔一段时间就会收到总线 10 运行时错误的原因？

作业是编写一个石头剪刀布游戏，这就是我的想法。

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

char* getUserChoice() 
{
    /* Prompt the user "Enter rock, paper, or scissors: " and return
       the string they enter */
    printf("Enter rock, paper, or scissors: ");
    char * uChoice = malloc(sizeof(char) * 128);
    scanf("%s", uChoice);
    return uChoice;
}

char* getComputerChoice() 
{
    srand (time(NULL));
    /* get a pseudo-random integer between 0 and 2 (inclusive) */
    int randChoice = rand() % 3;
    char * cpuChoice = malloc(sizeof(char) * 128);
    /* If randChoice is 0, return "rock", otherwise if randChoice is 1, 
       return "paper", and if randChoice is 2, return "scissors". */
    if (randChoice == 0)
        cpuChoice = "rock";
    else if (randChoice == 1)
        cpuChoice = "paper";
    else
        cpuChoice = "scissors";
    return cpuChoice;
}

char* compare(char* choice1, char* choice2) 
{
    /* Implement the logic of the game here. If choice1 and choice2
    are equal, the result should be "This game is a tie."
    Make sure to use strcmp for string comparison.*/

    char * cmpChoice = malloc(sizeof(char) * 128);
    int comparedValue = strcmp(choice1,choice2);
    if (comparedValue == 0)
        cmpChoice = "This game is a tie.";        
    else
    {
        if ((strcmp(choice1, "rock") == 0 && strcmp(choice2, "paper") == 0) || 
            (strcmp(choice1,"paper") == 0 && strcmp(choice2, "scissors") == 0) || 
            (strcmp(choice1, "scissors") == 0 && strcmp(choice2, "rock") == 0))
          cmpChoice = strcat(choice2, " wins");
        else
            strcat(choice1, " wins);
    }
    return cmpChoice;
}

int main(int argc, char** argv) 
{
    char *userChoice, *computerChoice, *outcome;

    userChoice = getUserChoice();
    computerChoice = getComputerChoice();
    outcome = compare(userChoice, computerChoice);

    printf("You picked %s.\n", userChoice);
    printf("Computer picked %s\n", computerChoice);
    printf("%s\n", outcome);
    return 0;
}

我描述的奇怪行为有时输出会像这样

Enter rock, paper, or scissors: paper
You picked paper wins..       // why is it saying "You picked paper wins.."
Computer picked rock
paper wins.

其他时候无需重新编译即可

Enter rock, paper, or scissors: scissors
Bus error: 10 // possibly due to not calling free()?

如果有人可以帮助我了解如何在返回指针之前释放分配的内存，那就太好了。显然，仅使用字符串会更容易，但要求使用 char * 类型。

感谢您提供的所有帮助或见解。

使用更新的代码进行编辑

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

char* getUserChoice() 
{
    /* Prompt the user "Enter rock, paper, or scissors: " and return
       the string they enter */
    printf("Enter rock, paper, or scissors: ");
    char * uChoice = malloc(sizeof(char) * 128);
    scanf("%s", uChoice);
    return uChoice;
}

char* getComputerChoice() 
{
    srand (time(NULL));
    /* get a pseudo-random integer between 0 and 2 (inclusive) */
    int randChoice = rand() % 3;
    char * cpuChoice = malloc(sizeof(char) * 128);
    /* If randChoice is 0, return "rock", otherwise if randChoice is 1, 
       return "paper", and if randChoice is 2, return "scissors". */
    if (randChoice == 0)
        strcpy(cpuChoice, "rock");
    else if (randChoice == 1)
        strcpy(cpuChoice, "paper");
    else
        strcpy(cpuChoice, "scissors");
    return cpuChoice;
}

char* compare(char* choice1, char* choice2) 
{
    /* Implement the logic of the game here. If choice1 and choice2
    are equal, the result should be "This game is a tie."
    Make sure to use strcmp for string comparison.*/

    char * cmpChoice = malloc(sizeof(char) * 128);
    int comparedValue = strcmp(choice1,choice2);
    if (comparedValue == 0)
        strcpy(cmpChoice, "This game is a tie.");        
    else
    {
        if ((strcmp(choice1, "rock") == 0 && strcmp(choice2, "paper") == 0) || 
            (strcmp(choice1,"paper") == 0 && strcmp(choice2, "scissors") == 0) || 
            (strcmp(choice1, "scissors") == 0 && strcmp(choice2, "rock") == 0))
        {
            strcat(cmpChoice, choice2);
            strcat(cmpChoice, " wins");
        }
        else
        {          
            strcat(cmpChoice, choice1);
            strcat(cmpChoice, " wins.");
        }
    }
    return cmpChoice;
}

int main(int argc, char** argv) 
{
    char *userChoice, *computerChoice, *outcome;

    userChoice = getUserChoice();
    computerChoice = getComputerChoice();
    outcome = compare(userChoice, computerChoice);

    printf("You picked %s.\n", userChoice);
    printf("Computer picked %s\n", computerChoice);
    printf("%s\n", outcome);
    return 0;
}

所以，非常感谢大家的评论。我已经修复了代码上的一些地方，并且它似乎可以编译和运行，没有错误。现在，我试图弄清楚何时free() 分配的内存。我显然无法在返回后释放它，但我需要返回该值。

我是否可以将其复制到 char，然后释放分配的原始内存？

再次感谢

Answer 1

您不需要使用malloc。只需将一个 char 指针传递给该方法，而不是返回一个。

void getUserChoice(char * choice)
{
    /* Prompt the user "Enter rock, paper, or scissors: " and return
       the string they enter */
    printf("Enter rock, paper, or scissors: ");
    scanf("%s", choice);
}

然后在 main 中像这样使用它...

char uChoice[128];
getUserChoice(uChoice);