read读指针自动后移

本文展示了一个使用C++进行文件读取的实例,详细解释了如何通过系统调用open, read和close来逐字节读取文件内容,并展示了实际运行结果。通过对代码的解析,读者可以了解到C++中文件操作的具体实现。

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以下为测试样例cpp文件,

 

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#include <unistd.h>

#include <sys/stat.h>

#include <fcntl.h>

#include <stdlib.h>

#include <iostream>

 

using namespace std;

 

int main()

{

   char c;

   int in, out,nread;

   int addint = 0;

   in = open("file.in",O_RDONLY);

   //cout << in;

   out = open("file.out",O_WRONLY|O_CREAT, S_IRUSR|S_IWUSR);

   while((nread=read(in,&c,1))>-2 && addint  != 10 )

   {

cout<<"number of read:"<<nread<<"; ";

        cout<<"and the character is :"<<c<<endl;

        addint++;

//write(out,&c,1);

   }

  exit(0);

 

}

 

其中file.in的文件内容为

 

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[root@localhost cpp]# cat file.in

abcd

 

 

编译运行:

 

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[root@localhost cpp]# g++ copy_system.cpp -o copy_system

[root@localhost cpp]# ./copy_system

number of read:1; and the character is :a

number of read:1; and the character is :b

number of read:1; and the character is :c

number of read:1; and the character is :d

number of read:1; and the character is :

 

number of read:0; and the character is :

 

number of read:0; and the character is :

 

number of read:0; and the character is :

 

number of read:0; and the character is :

 

number of read:0; and the character is :

经过测试发现,此程序能完整读出文件内容,而不是循环只读出同一个字符,说明读指针会自动后移

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