函数内部数组的realloc结构

时间:2013-10-18 18:54:00

标签: c dynamic struct malloc realloc

我制作了一个库程序,用于在我的struct数组中存储电影并使用动态内存分配,但没有成功。添加第一个记录(电影)工作正常,但在第二个记录之后,值只是混乱的字符。

除了展示我的代码之外,没有什么可说的。

问题是我无法在realloc

内部addmovie();

但是,如果我把这一行:

movie = (struct movies *) realloc(movie, (records+1) * sizeof(struct movies)); 

在调用addmovie();函数之前,它似乎有效,为什么?

/* Global variables */
int records = 0; // Number of records

struct movies{
    char name[40];
    int id;
};

addmovie(struct movies **movie)
{
    int done = 1;
    char again;
    int index;

    while (done)
    {
        index = records;
        records++; // Increment total of records

        struct movies *tmp = (struct movies *) realloc(movie, (records+1) * sizeof(struct movies));

        if (tmp)
            *movie = tmp;

        system("cls");
        fflush(stdin);
        printf("Enter name of the Movie: ");
        fgets(movie[index].name, 40, stdin);

        fflush(stdin);
        printf("Enter itemnumber of the Movie: ");
        scanf("%d", &movie[index].id);

        printf("\nSuccessfully added Movie record!\n");

        printf("\nDo you want to add another Movie? (Y/N) ");
        do
        {
            again = getch();
        } while ( (again != 'y') && (again != 'n') );

        switch ( again )
        {
        case ('y'):
            break;

        case ('n'):
            done = 0;
            break;
        }
    } // While
}

int main()
{
    int choice;

    struct movies *movie;
    movie = (struct movies *) malloc(sizeof(struct movies)); // Dynamic memory, 68byte which is size of struct

    while (done)
    {
        system("cls");
        fflush(stdin);
        choice = menu(); //returns value from menu

        switch (choice)
        {
        case 1:
            addmovie(movie);
            break;
        }

    } // While

    free(movie); // Free allocated memory
    return 0;
}

1 个答案:

答案 0 :(得分:3)

C是一种按值传递的语言。当你这样做时:

movie = (struct movies *) realloc(movie, (records+1) * sizeof(struct movies));

在您的功能中,来自movie的{​​{1}}完全不受影响。你需要传递一个指向指针的指针:

main()

然后修改指针的内容:

void addmovie(struct movies **movie)

请注意,不要将struct movies *tmp = realloc(...) if (tmp) *movies = tmp; 的返回值分配给要传递给它的变量也很重要 - 最终可能会泄漏。

查看comp.lang.c FAQ question 4.8以获取完整说明。