C++ and C file I/O

Question

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 Can anyone please tell are the

Answer 1

Banishing buffer overruns seems like a big win for C++ to me.

Answer 2

The performance differences between printf()/fwrite style I/O and C++ IO streams formatting are very much implementation dependent. Some implementations (visual C++ for instance), build their IO streams on top of FILE * objects and this tends to increase the run-time complexity of their implementation. Note, however, that there was no particular constraint to implement the library in this fashion.

In my own opinion, the benefits of C++ I/O are as follows:

• Type safety as already stated earlier.
• Flexibility of implementation. Code can be written to do specific formatting or input to or from a generic ostream or istream object. The application can then invoke this code with any kind of derived stream object. If the code that I have written and tested against a file now needs to be applied to a socket, a serial port, or some other kind of internal stream, you can create a stream implementation specific to that kind of I/O. Extending the C style I/O in this fashion is not even close to possible.
• Flexibility in locale settings: the C approach of using a single global locale is, in my opinion, seriously flawed. I have experienced cases where I invoked library code (a DLL) that changed the global locale settings underneath my code and completely messed up my output. A C++ stream allows you to imbue() any locale to a stream object.

Answer 3

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

Answer 4

Please have a look at

http://www.ddj.com/cpp/184403651

then You will prefer C++ I/O than C I/O.

in short C is prefered if you know data size prior to read or write and for speed. C++ is prefered if you don't know data size and for efficient code.

Answer 5

std::ifstream and std::ofstream are already in stl library. You don't have to create your own.

The main benefit is all outputs and inputs are type safety.

Answer 6

Whenever I need to take inputs/give outputs in a file in C++, I just use two lines.

freopen("input.txt","r",stdin); // for input from file
freopen("output.txt","w",stdout);// for output from file

Now you can scan variables as you would normally do from console, and whatever you print as output will be displayed in output.txt file.

So I don't think file I/O in c++ is tough, its rather easier than c.