CODEWITHSUNDEEP
cfwrite
fwriteErr
fwriteErr

Reputation: 73

C++ fwrite() writes more than expected

I have problem when copying files

code:

    bool done;
    FILE* fin;
    FILE* fout;
    const int bs = 1024*64;//64 kb
    char* buffer[bs];
    int er, ew, br, bw;
    long long int size = 0;
    long long int sizew = 0;
    er = fopen_s(&fin,s.c_str(),"rb");
    ew = fopen_s(&fout,s2.c_str(),"wb");
    if(er == 0 && ew == 0){
        while(br = fread(buffer,1,bs,fin)){
            size += br;
            sizew += fwrite(buffer,1,bs,fout);
        }
        done = true;
    }else{
        done = false;
    }
    if(fin != NULL)fclose(fin);
    if(fout != NULL)fclose(fout);

Somehow fwrite writes whole buffer ignoring count value (br)

Some examples how:

Copying 595 file of 635 DONE. 524288/524288 B
Copying 596 file of 635 DONE. 524288/524288 B
Copying 597 file of 635 DONE. 65536/145 B
Copying 598 file of 635 DONE. 65536/16384 B
Copying 599 file of 635 DONE. 65536/145 B
Copying 600 file of 635 DONE. 65536/67 B
Copying 601 file of 635 DONE. 65536/32768 B
Copying 602 file of 635 DONE. 65536/67 B

Anyone knows where is the problem?

Upvotes: 3

Views: 221

Answers (2)

Lightness Races in Orbit
Lightness Races in Orbit

Reputation: 385385

ignoring count value (br)

Actually you wrote bs.

A good example of the dangers of poor variable naming!

Upvotes: 7

StilesCrisis
StilesCrisis

Reputation: 16310

You should do

        sizew += fwrite(buffer,1,br,fout);

You were passing bs, which was the maximum amount that fread was allowed to read. br was the amount that fread actually did read.

Upvotes: 5

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