Unformatted binary file input

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C++

#include <iostream>
#include <fstream>

using namespace std;

int main()
{
	ofstream out("f.bin");
	char c = 0x61;
	out.write(&c, sizeof(char));

	ifstream in("f.bin");
	char d;
	in.read(&d, sizeof(char));
	if (d != 0x61) cerr << "Extraction failed!" << endl; //this always appears

	return 0;
}

This is a simplified snippet of my attempt in a practice of dealing with binary file i/o. The hex editor shows that writing is successful ('a' in f.bin), but I have no idea why I cannot extract the char from the file (). What did I miss here?

Posted 15-Jun-15 16:20pm

Member 11212276

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PIEBALDconsult 15-Jun-15 22:30pm

Dunno. Maybe the buffer didn't get flushed? Can you type the file to the console and see the character?

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User 59241 · Accepted Answer · 2015-06-15T16:46:00

Solution 1

Try:

C++

int main()
{
	ofstream out("test.bin", ofstream::out);

	char c = 0x61;
	out.write(&c, sizeof(char));

	out.close();
 
	ifstream in("test.bin", ofstream::in);
	char d;
	in.read(&d, sizeof(char));
	if (d != 0x61) cerr << "Extraction failed!" << endl; //this always appears
	in.close();

	return 0;
}

http://www.cplusplus.com/doc/tutorial/files/[^]

Posted 15-Jun-15 16:46pm

User 59241

Updated 15-Jun-15 16:49pm

v2

Comments

Member 11212276 15-Jun-15 23:11pm

Hmm since ofstream::out and ifstream::in are default mode, it's close that does the trick? So it's really buffer related issue? But I'm still confused how are buffers for ofstream and ifstream related? Do you mind explaining it to me as if to a dummy?:s

[no name] 15-Jun-15 23:19pm

Data is not written until the close(). Flush() should also work but close() is guaranteed. The link I added should explain it.