c语言copy函数兑现

#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;
}