linux下文件编程

对文件操作有两种方式：

 A、系统调用方式，这个是基于具体的操作系统

 B、调用C库函数方式

下面具体讲解这两种方式,以及用到的相关的函数；

A：系统调用（系统函数linux为例）

综合实例，用系统函数编程实现文件的拷贝：

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

#define MAX_SIZE 1024

void copy(char *from_file,char *to_file)
{
	int from_fd ;
	int to_fd;
	char buff[MAX_SIZE];
	int read_size;
	int write_size;
	if((from_fd = open(from_file,O_RDONLY))==-1)
	{
		printf("The file of %s don't exist!\n",from_file);
		exit(1);
	}
	if((to_fd=open(to_file,O_WRONLY|O_CREAT,0777))==-1)
	{
		printf("The file of %s don't exist!\n",to_file);
		exit(1);
	}
	while((read_size=read(from_fd,buff,MAX_SIZE))>0)
	{
		write_size = write(to_fd,buff,read_size);
		while(write_size<read_size)
		{
			read_size -= write_size;
			write_size += write(to_fd,buff,read_size);
		}

	}
	close(from_fd);
	close(to_fd);
}

int main(int argc, char *argv[])
{
	int i;
	char *from_file;
	char *to_file;
	if(argc!=3){
		printf("Please input a right expression\n");
		exit(1);
	}else{
		from_file = argv[1];
		to_file = argv[2];
		copy(from_file,to_file);
	}
	return 0;
}

B，用C库函数编程实现文件的拷贝

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAX_SIZE 1024

void copy(FILE *form_file,FILE *to_file);

int main(int argc,char *argv[])
{
	FILE *from_file;
	FILE *to_file;
	if(argc!=3){
		printf("Please input a right expression!\n");
		exit(1);
	}else{
		if((from_file=fopen(argv[1],"rb"))==NULL)
		{
			printf("Can't open the file of %s\n",argv[1]);
			exit(1);
		}
		
		if((to_file=fopen(argv[2],"wb"))==NULL)
		{
			printf("Can't open the file of %s!\n",argv[2]);
			exit(1);
		}
		
		copy(from_file,to_file);
	}
	return 0;
}

void copy(FILE *from_file,FILE *to_file)
{
	char buff[MAX_SIZE];

	long file_size;
	fseek(from_file,0L,SEEK_END);
	file_size = ftell(from_file);
	fseek(from_file,0L,SEEK_SET);
//	printf("The file size is:%d\n",file_size);	
	while(!feof(from_file))
	{
		memset(buff,0,MAX_SIZE);
		fread(buff,MAX_SIZE,1,from_file);
		if(file_size<MAX_SIZE){
			fwrite(buff,file_size,1,to_file);
		}else{
			fwrite(buff,MAX_SIZE,1,to_file);
			file_size -= MAX_SIZE; 
		}	
	}
	fclose(from_file);
	fclose(to_file);
}