c语言copy函数实现

#include <stdio.h>#include <stdlib.h>#include <string.h>#include<unistd.h>#include<sys/types.h>#include<sys/stat.h>#include<fcntl.h>int readFile(char *fname,char *buff);int writeFile(char *fname,char *buff);int main(int argc,char *argv[]){    FILE *fd;    int i;    int ch;    char *buf = NULL;    buf = (char*)malloc(sizeof(char)*1024*1000*20);        if(argc != 3)    {        printf("Usage copy source dest\n");        exit(1);    }        if(access(argv[1],R_OK|F_OK) < 0)    {        printf("%s cannot read or file not found！",argv[1]);        exit(1);    }        if(strcmp(argv[1],argv[2]) == 0)    {        printf("%s cannot copy the same file！",argv[1]);        exit(1);        }        readFile(argv[1],buf);    writeFile(argv[2],buf);    }/** 读源文件 **/int readFile(char *fname,char *buff)  {      FILE *fp;      char ch;      int i=0;        if((fp=fopen(fname,"rb")) == NULL)      {          perror("open log file error");        return -1;    }        while(!feof(fp))    {        ch=fgetc(fp);          buff[i]=ch;        i++;    }        buff[i] = '\0';    fclose(fp);        return 0;}/** 写入目标文件 **/int writeFile(char *fname,char *buff){    int fd;    size_t len;        if((fd = open(fname,O_WRONLY|O_CREAT|O_TRUNC,S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH)) < 0)    {        perror("open log file error");        return -1;    }        len = strlen(buff);    printf("%c",len);    if(write(fd,buff,(int)len) < 1)    {        perror("write log error");        return -1;    }        close(fd);    return 0;}