用C语言编写文件复制程序。分别使用系统调用read (fd,buf,nbytes)、write(fd, buf,nbytes)和文件的库函数fread(buf,size,nitems,fp)、fwrite(buf,size,nitems,fp)，编写一个文件复制程序。

使用系统调用read和write实现文件复制程序：

#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>

#define BUF_SIZE 1024

int main(int argc, char *argv[]) {
    int source_fd, target_fd;
    ssize_t nread;
    char buf[BUF_SIZE];

    if (argc != 3) {
        fprintf(stderr, "Usage: %s source_file target_file\n", argv[0]);
        return 1;
    }

    source_fd = open(argv[1], O_RDONLY);
    if (source_fd == -1) {
        perror("open");
        return 1;
    }

    target_fd = open(argv[2], O_WRONLY | O_CREAT | O_TRUNC, 0644);
    if (target_fd == -1) {
        perror("open");
        return 1;
    }

    while ((nread = read(source_fd, buf, BUF_SIZE)) > 0) {
        if (write(target_fd, buf, nread) != nread) {
            perror("write");
            return 1;
        }
    }

    if (nread == -1) {
        perror("read");
        return 1;
    }

    if (close(source_fd) == -1) {
        perror("close");
        return 1;
    }

    if (close(target_fd) == -1) {
        perror("close");
        return 1;
    }

    return 0;
}

使用文件的库函数fread和fwrite实现文件复制程序：

#include <stdio.h>

#define BUF_SIZE 1024

int main(int argc, char *argv[]) {
    FILE *source_fp, *target_fp;
    size_t nread;
    char buf[BUF_SIZE];

    if (argc != 3) {
        fprintf(stderr, "Usage: %s source_file target_file\n", argv[0]);
        return 1;
    }

    source_fp = fopen(argv[1], "rb");
    if (source_fp == NULL) {
        perror("fopen");
        return 1;
    }

    target_fp = fopen(argv[2], "wb");
    if (target_fp == NULL) {
        perror("fopen");
        return 1;
    }

    while ((nread = fread(buf, 1, BUF_SIZE, source_fp)) > 0) {
        if (fwrite(buf, 1, nread, target_fp) != nread) {
            perror("fwrite");
            return 1;
        }
    }

    if (ferror(source_fp)) {
        perror("fread");
        return 1;
    }

    if (fclose(source_fp) != 0) {
        perror("fclose");
        return 1;
    }

    if (fclose(target_fp) != 0) {
        perror("fclose");
        return 1;
    }

    return 0;
}