C ++和C文件I / O [英] C++ and C file I/O

问题描述

C ++文件I / O比C文件I / O强。
那么在C ++中，为文件I / O创建一个新的库是有用的还是不？我的意思是< fstream>
任何人都可以告诉C ++文件I / O有什么好处吗？

解决方案

意见

我不知道有什么真正的项目使用C ++流。他们太慢，很难使用。有几个较新的库，如 FastFormat 和 Boost 版本声称更好在最后一个ACCU Overload杂志上有一篇关于他们。个人而言，我在C ++中使用了c FILE库，过去15年左右，我看不到有任何改变的理由。

速度

这里是小测试程序（我一起敲快）显示基本速度问题：

  #include< stdio.h> 
 #include< time.h> 
 
＃include< iostream> 
＃include< fstream> 
 
 using namespace std; 
 
 int main（int argc，const char * argv []）
 {
 const int max = 1000000; 
 const char * teststr =example; 
 
 int start = time（0）; 
 FILE * file = fopen（example1，w）; 
 for（int i = 0; i  {
 fprintf（file，％s：％d\\\
，teststr，i） 
} 
 fclose（file）; 
 int end = time（0）; 
 
 printf（C FILE：％ds \\\
，end-start）; 
 
 start = time（0）; 
 ofstream outdata; 
 outdata.open（example2.dat）; 
 for（int i = 0; i  {
 outdata<测试< ：<< i<< endl; 
} 
 outdata.close（）; 
 end = time（0）; 
 
 printf（C ++ Streams：％ds \\\
，end-start）; 
 
 return 0; 
} 
  

我的电脑上的结果：

  C文件：5s 
 C ++流：260s 
 
进程返回0（0x0）执行时间：265.282 s 
按任意键继续。 
  

我们可以看到，这个简单的例子是52x更慢。

注意：在我的示例中将endl更改为\\\
改进的C ++流它只比FILE *流慢3倍（感谢 jalf ），可能有办法使其更快。

难以使用

我不能认为printf（）不是简洁，

  double pi = 
 3.14285714; 
 
 cout<< pi =<< setprecision（5）<< pi<< '\\\
'; 
 printf（％.5f \\\
，pi）; 
 
 cout<< pi =<<固定<展示< setprecision（3）<< pi<< '\\\
'; 
 printf（％+。3f \\\
，pi）; 
 
 cout<< pi =<<科学< noshowpos< pi<< '\\\
'; 
 printf（％e \\\
，pi）; 
  

问题

是的，可能需要一个更好的C ++库，许多都是 FastFormat 是图书馆，只有时间会告诉。 / p>

dave

C++ file I/O is tougher than C file I/O. So in C++, creating a new library for file I/O is useful or not? I mean <fstream> Can anyone please tell are there any benefits in C++ file I/O ?

解决方案

Opinion

I don't know of any real project that uses C++ streams. They are too slow and difficult to use. There are several newer libraries like FastFormat and the Boost version that claim to be better there was a piece in the last ACCU Overload magazine about them. Personally I have used the c FILE library for the last 15 years or so in C++ and I can see no reason yet to change.

Speed

Here is small test program (I knock together quickly) to show the basic speed problem:

#include <stdio.h>
#include <time.h>

#include<iostream>
#include<fstream>

using namespace std;

int main( int argc, const char* argv[] )
    {
    const int max = 1000000;
    const char* teststr = "example";

    int start = time(0);
    FILE* file = fopen( "example1", "w" );
    for( int i = 0; i < max; i++ )
        {
        fprintf( file, "%s:%d\n", teststr, i );
        }
    fclose( file );
    int end = time(0);

    printf( "C FILE: %ds\n", end-start );

    start = time(0);
    ofstream outdata;
    outdata.open("example2.dat");
    for( int i = 0; i < max; i++ )
        {
        outdata << teststr << ":" << i << endl;
        }
    outdata.close();
    end = time(0);

    printf( "C++ Streams: %ds\n", end-start );

    return 0;
    }

And the results on my PC:

C FILE: 5s
C++ Streams: 260s

Process returned 0 (0x0)   execution time : 265.282 s
Press any key to continue.

As we can see just this simple example is 52x slower. I hope that there are ways to make it faster!

NOTE: changing endl to '\n' in my example improved C++ streams making it only 3x slower than the FILE* streams (thanks jalf) there may be ways to make it faster.

Difficulty to use

I can't argue that printf() is not terse but it is more flexible (IMO) and simpler to understand, once you get past the initial WTF for the macro codes.

double pi = 3.14285714;

cout << "pi = " << setprecision(5)  << pi << '\n';
printf( "%.5f\n", pi );

cout << "pi = " << fixed << showpos << setprecision(3) << pi << '\n'; 
printf( "%+.3f\n", pi );

cout << "pi = " << scientific << noshowpos << pi<< '\n';
printf( "%e\n", pi );

The Question

Yes, may be there is need of a better C++ library, many be FastFormat is that library, only time will tell.

dave

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