C++: reading large pgm file with ifstream

Question

I want to load a 16-bit binary PGM image with a size of 4096x4096 pixels using std::ifstream. The problem is that I can only load smaller files, eg. 512x512. If I try to load the "large" one the data I get is always 0 for every pixel.

Example Code:

int size = width*height;
unsigned short* data = new unsigned short[size];

// Read the terrain data
for(int i = 0; i < size; i++)
{
    file >> data[i];
}

If I set size manually to a lower value, this seems to work. Any idea?

Thx Tim

Presumably this is binary data. Read it as binary with `fstream.read()`. Op>> likely fails early on and you don't know it. — Duck, Jun 30 '13 at 15:09
Duck has a point, `operator >>` should not be used to extract binary data. — David G, Jun 30 '13 at 15:25

score 1 · Accepted Answer · answered Jun 30 '13 at 15:58

1

operator >> should not be used for binary extraction operations. Instead, by using read the file will simply input the bytes:

file.read(reinterpret_cast<char*>(data), sizeof data);

answered Jun 30 '13 at 15:58

David G

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C++: reading large pgm file with ifstream

1 Answers1