写一个函数实现文件拷贝功能

#include<stdio.h>

int main(int argc,char *argv[])
{
　　　　char buf[100]={0};
    if(argc<3){
        printf("参数输入错误
");
        return 0;
    }

    FILE *p_src = fopen(argv[1],"rb");
    if(!p_src){
        printf("读取文件失败
");
        return 0;
    }

    FILE *p_dst = fopen(argv[2],"wb");
    if(!p_dst){
        printf("写入文件失败
", );
        fclose(p_src);
        p_src = NULL;
        return 0;
    }

    int size = 0;
    while(1){
        size = fread(buf,sizeof(char),100,p_src);
        if(!size)
            break;
        fwrite(buf,sizeof(char),size,p_dst);
    }
    
    fclose(p_dst);
    p_dst = NULL;
    fclose(p_src);
    p_src = NULL;

}

还可以运用系统调用函数实现cat命令的功能：

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include<stdio.h>
#include<unistd.h>
#define MAXSIZE 4096
int main(int argc,char *argv[])
{
    char buf[MAXSIZE];
    size_t n = 0;
    int fd = open(argv[1],O_RDONLY);
    if(fd==-1){perror("open");return -1;}

    while((n = read(fd,buf,MAXSIZE))>0){
        if(write(1,buf,n)!=n){
            printf("write error");
            return 0;
        }
    }

    close(fd);
    return 0;
}