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?
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 ?
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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