Question

我正在尝试初始化我的struct中的一些变量，但是当我将前变量赋值为零时，我遇到了一个seg错误。特别是newBuff-＆gt; front = 0;

typedef struct buffer{
    pthread_mutex_t lock;
    pthread_cond_t shout;
    int front;
    int rear;
    char bytes[1024];
} buffer;

int main(int argc, char const *argv[]) {
    FILE *file = fopen(argv[1], "r");
    if (argc != 2){
        printf("You must enter in a file name\n");
    }
    printf("%lu\n", sizeof(file));
    int shmid;
    char path[] = "~";
    key_t key = ftok(path, 7);
    shmid = shmget(key, SIZE, 0666 | IPC_CREAT | IPC_EXCL); //shared memory creation
    buffer* newBuff = (buffer*) shmat(shmid, 0, 0);
    newBuff->front = 0;

Answer 1

您未检查newBuff返回的shmat()的值，以确保其无效，例如： (void*) -1（按http://man7.org/linux/man-pages/man2/shmop.2.html）。您还需要检查shmget()的返回值，以确保它在第一时间成功。

几乎可以肯定，newBuff为-1，尝试取消引用会给你一个段错误。

Answer 2

我能看到的几件事：

错误控制参数。你正在检查它们，但是你要退出程序吗？ ;）
当您将函数调用为shmat时，您不会检查结果。查看手册（man shmat）。

上面说的，我看不到你的整个代码，但这是我的建议：

typedef struct buffer{
    pthread_mutex_t lock;
    pthread_cond_t shout;
    int front;
    int rear;
    char bytes[1024];
} buffer;

int main(int argc, char const *argv[]) {
    int shmid = -1;
    FILE *file = NULL;
    if (argc != 2){
        printf("You must enter in a file dumbass\n");
        // And you must terminate here your program!
        return 1;
    }
    file = fopen(argv[1], "r");
    // Another check that you are not making and can raise a SIGVSEG
    if (file == NULL) {
        printf("The file '%s' can not be opened\n", argv[1]);
        return 1;
    }
    printf("File size: %lu\n", sizeof(file));
    char path[] = "~";
    key_t key = ftok(path, 7);
    // Another check
    if (key == -1) {
        fclose(f);
        printf("The path '%s' does not exist or cannot be accessed\n", path);
        return 1;
    }
    shmid = shmget(key, SIZE, 0666 | IPC_CREAT | IPC_EXCL);
    // One more check
    if (shmid == -1) {
        fclose(f);
        printf("An error happened getting shared memory identifier\n");
        return 1;
    }
    buffer* newBuff = (buffer*)shmat(shmid, 0, 0);
    // And finally! Another potential source that could raise a SIGVSEG
    if (buffer == NULL) {
        fclose(f);
        printf("An error happened getting the shared memory area\n");
        return 1;
    }
    newBuff->front = 0;

请！检查每次返回的功能！你无法想象会发生多少真正的问题，因为不良的做法不能正确检查这些回报。

分配结构变量

2 个答案: