通過結構函數作爲空指針

Question

我試圖將一個結構的指針傳遞給一個函數，但是當我嘗試訪問該結構時，結構中的最後一個變量缺少1字節的內存地址導致任何使用可變段錯誤。

typedef struct 
{ 
    pthread_t tID; 
    int tType; 
}sThread; 

sThread threads[MAX_THREADS]; 

typedef struct 
{ 
    int tID; 
    int sock; 
    int arg_count; 
    char *from_p, **arg_p; 
}command_struct; 

pthread_t Thread_Start(void *function, void *param) 
{ 
    pthread_t tHandle; 

    pthread_create(&tHandle, NULL, function, (void*)param); 

    return tHandle; 
} 

void cmd_test(int sock, char *from_p, char **arg_p, int arg_count) 
{ 
    if(thread_check(1)) 
    { 
    send_line(sock, "%s :test thread already running", from_p); 
    return; 
    } 

    command_struct test; 

    test.tID = thread_add(1); 
    test.arg_count = arg_count; 
    test.arg_p = arg_p; 

    threads[test.tID].tID = Thread_Start(test_cmd, &test); 
} 

void *test_cmd(void *param) 
{ 
    command_struct test = *((command_struct *)param); 

    int i = 0; 

    for(i = 1; i < test.arg_count; i++) 
    { 
    printf("%s", test.arg_p[i]); 
    } 

    thread_clear(test.tID); 
    return NULL; 
} 

正在發生的事情是內部cmd_test（功能產卵的線程）結構被正確初始化，所有的變量是正確的。

$1 = {tID = 0, sock = 5, arg_count = 5, from_p = 0xbffff254 "test", arg_p = 0xbfffec48} 

但從withing test_cmd這是一個正在運行的內螺紋的結構法缺少1個字節關閉導致arg_p地址：

$1 = {tID = 0, sock = 5, arg_count = 5, from_p = 0xbffff254 "test", arg_p = 0xffec48} 

如果我一個無用的變量添加到我的command_struct arg_p的地址結束然後變得正確，並且command_struct中的最後一個變量缺少內存地址的1個字節。

Answer 1

您正在向您的線程傳遞一個指向局部變量的指針 - 在線程訪問它時，內存已被重用用於其他事情。

試試這個：

void cmd_test(int sock, char *from_p, char **arg_p, int arg_count) 
{ 
    if(thread_check(1)) 
    { 
     send_line(sock, "%s :test thread already running", from_p); 
     return; 
    } 

    // === begin modified code in cmd_test(): 
    command_struct* test = malloc(sizeof(command_struct)); 

    test->tID = thread_add(1); 
    test->arg_count = arg_count; 
    test->arg_p = arg_p; 

    threads[test.tID].tID = Thread_Start(test_cmd, test); 
    // === end modified code 
} 

void *test_cmd(void *param) 
{ 
    command_struct test = *((command_struct *)param); 
    free(param); // <-- new line of code 

    // remainder is the same... 
    // ... 
}