如何强制fseek（）移动光标(How to force fseek() to move the cursor)

 我有一个程序，它创建多个线程，每个线程尝试在不同位置（偏移）的文件中写入100个字节。 第一个线程从0开始写入100个字节，从100开始写入第二个100个字节，从300开始写入第三个100个字节，依此类推如果线程按此顺序执行，则可以使用，并且我不需要fseek。 但是对于实时并发，如果我将第一个线程置于“sleep（2）”2秒钟，等待所有其他线程完成，并使用fseek将文件光标移动到文件的开头，这不会发生。 我使用互斥锁来处理并发。 代码示例： 
 
    offset=0;//for the first thread
    char data[100];
    int length; // how many chars are currently in data
    FILE * f;

    pthread_mutex_lock(&mutexFileWrite);
    f = fopen(fileName, "a");
    fseek(f,offset, SEEK_SET);  
    fwrite(data,sizeof(char),length,f);
    fclose(f);
    pthread_mutex_unlock(&mutexFileWrite);

I have a program which creates multiple threads and each one of them tries to write 100 bytes in a file at a different location(offset). The first thread writes 100 bytes starting from 0, the second 100 bytes starting from 100, the third 100 bytes starting from 300 and so on If the threads are executed in this order everithing is ok and I do not need fseek. But for real time concurrency if I put the first thread to "sleep(2)" for 2 seconds, wait until all other threads are done, and use fseek to move the file cursor to the begining of the file this doesn't happen. I used mutexes to handle concurrency. Code sample:
 
    offset=0;//for the first thread
    char data[100];
    int length; // how many chars are currently in data
    FILE * f;

    pthread_mutex_lock(&mutexFileWrite);
    f = fopen(fileName, "a");
    fseek(f,offset, SEEK_SET);  
    fwrite(data,sizeof(char),length,f);
    fclose(f);
    pthread_mutex_unlock(&mutexFileWrite);

原文：https://stackoverflow.com/questions/14081265