C语言写一个双线程文件复制程序

在C语言中编写一个双线程文件复制程序可以利用POSIX线程库(pthread)。下面是一个简单的示例，它创建两个线程分别负责读取源文件和写入目标文件：

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <unistd.h>

#define BUF_SIZE 4096
char src[50], dst[50];
size_t bytes_read, bytes_written;

// 读取数据的线程函数
void* read_thread(void* arg) {
    FILE *src_file = fopen(src, "rb");
    if (!src_file) {
        perror("Error opening source file");
        return NULL;
    }

    while (bytes_read != EOF) {
        char buffer[BUF_SIZE];
        size_t read = fread(buffer, sizeof(char), BUF_SIZE, src_file);
        if (read == 0)
            break;
        bytes_read += read;
        pthread_mutex_lock(&mutex); // 线程同步
        fwrite(buffer, sizeof(char), read, dst_file);
        pthread_mutex_unlock(&mutex);
    }
    fclose(src_file);
    return NULL;
}

// 写入数据的线程函数
void* write_thread(void* arg) {
    FILE *dst_file = fopen(dst, "wb");
    if (!dst_file) {
        perror("Error opening destination file");
        return NULL;
    }

    while (bytes_written != bytes_read) {
        char buffer[BUF_SIZE];
        size_t written = fread(buffer, sizeof(char), BUF_SIZE, stdin); // 模拟从缓冲区读取
        if (written == 0)
            break;
        bytes_written += written;
        pthread_mutex_lock(&mutex);
        fwrite(buffer, sizeof(char), written, dst_file);
        pthread_mutex_unlock(&mutex);
    }
    fclose(dst_file);
    return NULL;
}

int main() {
    pthread_mutex_init(&mutex, NULL);

    printf("Enter the source file path: ");
    fgets(src, sizeof(src), stdin);
    src[strlen(src)-1] = '\0'; // 移除换行符

    printf("Enter the destination file path: ");
    fgets(dst, sizeof(dst), stdin);
    dst[strlen(dst)-1] = '\0';

    pthread_t reader, writer;
    if (pthread_create(&reader, NULL, read_thread, NULL) || pthread_create(&writer, NULL, write_thread, NULL)) {
        perror("Error creating thread");
        exit(1);
    }

    pthread_join(reader, NULL);
    pthread_join(writer, NULL);

    pthread_mutex_destroy(&mutex);
    return 0;
}

在这个例子中，`read_thread` 和 `write_thread` 分别读取源文件和将内容写入目标文件，通过共享全局变量`bytes_read` 和 `bytes_written` 来同步进程。注意，这个示例简化了输入和同步过程，实际应用中需要更完善的错误处理和用户交互。