C：多個pthread期間fgets錯誤

Question

該程序的總體目標是從文件中讀取數據（浮點型或字母），並使用互斥鎖更改全局常量。 （到目前為止，我還沒有應用它）

但是在我做之前，我只是想創建一個基本程序來讀取文件的全部內容並打印到屏幕上。 目前，我的程序無法執行此操作。 它只是讀取文件的第一個字符並退出文件。
我正在提供我的代碼以及錯誤。 任何幫助都會非常有幫助。

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

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
char *files[] = {"one.in", "two.in", "three.in", "four.in", "five.in"};

void* thread( void * arg )
{
    char * file = (char *) arg;
    // open the file and read the content
    FILE *fp = fopen(file,"r");
    char line[1024];
    int len;

    printf("Thread id is %s enter\n",file);
    if( !fp)
    {
        printf("%s file open failed\n", file);
        return 0;
    }
    else
        printf("%s File open success %p %d\n", file, fp, ftell(fp));
    // dump the file content with thread id (file name)
    while (fgets(line,len, fp))
    {
        printf("%s %s", file, line);
    }
    printf("Thread id is %s %d exit\n",file, ftell(fp));
    fclose(fp);
    return 0;
}

int main( void )
{
    int i = 0;

    if (pthread_mutex_init(&mutex, NULL) != 0)
    {
        printf("\n mutex init failed\n");
        return 1;
    }
    for(i = 4; i >= 0; i--)
    {
        pthread_t  id;
        pthread_create( &id, NULL, &thread, files[i] );
        pthread_detach(id);
    }
    printf("Main thread exit\n");
    pthread_exit(0);
    printf("Main thread real exit\n");
    return 0;
}

---

失誤

Thread id is five.in enter
five.in File open success 0x7fff7a2e7070 0
Thread id is five.in 0 exit
Thread id is four.in enter
four.in File open success 0x7fff7a2e7070 0
Thread id is four.in 0 exit
Thread id is three.in enter
three.in File open success 0x7fff7a2e7070 0
Thread id is three.in 0 exit
Thread id is two.in enter
two.in File open success 0x7fff7a2e7070 0
Thread id is two.in 0 exit
Thread id is one.in enter
one.in File open success 0x7fff7a2e7070 0
Thread id is one.in 0 exit
Main thread exit

---

文件格式

R
1
2
3
-4
-5
4
W

Answer 1

問題是對fgets()的調用：

while (fgets(line,len, fp))

len未初始化。 這是技術上不確定的行為 。

您想要的是使用line的大小：

while (fgets(line, sizeof line, fp))