Search code examples
c++file-ioifstream

Why does ifstream read() behave differently in two different programs?

I'm trying to write a program that reads in an OpenGL shader from a .txt file. I've actually already done this a few days ago, this was the code I used:

char vShaderData[2000];
char fShaderData[2000];
void readShaders() {
    std::ifstream vShaderF;
    std::ifstream fShaderF;
    vShaderF.open("shaders//vertexShader.txt");
    fShaderF.open("shaders//fragShader.txt");
    if (vShaderF.is_open() && fShaderF.is_open()) std::cout << m << "Shader read success" << std::endl; 
    else std::cout << "Shader read fail" << std::endl; 
    std::cout << m << "vertex shader: " << std::endl;
    vShaderF.read(vShaderData, 2000);
    for (int i = 0; i < 2000; i++) {
        std::cout << vShaderData[i];
    }
    std::cout << std::endl << std::endl;
    std::cout << m << "frag shader: " << std::endl;
    fShaderF.read(fShaderData, 2000);
    for (int i = 0; i < 2000; i++) {
        std::cout << fShaderData[i];
    }
    std::cout << std::endl;
    vShaderF.close();
    fShaderF.close();
}

This worked great. my shader file was not actually not 2000 in length, but the read() call seemed to store the extra characters as whitespace into the char array which is what I wanted.

Now having restructured my code a little bit in a newer program, my reader now looks like this:

    std::ifstream shaderFile;
    shaderFile.open(path);  
    if (shaderFile.is_open()) cout << "Shader at: " << path << ", initalized" << endl;
    char data[2000];
    shaderFile.read(data, 2000);

    for (int i = 0; i < 2000; i++) std::cout << data[i];

The actual text portion still reads correct. However, now the extra space in the char array is stored with this instead of whitespace: enter image description here

In case the image won't show, it is basically just a reapeating pattern of these two characters [|[|[|....

Why is this happening and how can I fix it?

NOTE: I'm using the same shader file, same computer, same IDE, same everything. The old one still works.

Solution

  • When using std::istream:read() it will not set the parts of the buffer to spaces which were not read. The memory will be left untouched. If you want to get spaces into an unread area of the buffer, you'll need to put the spaces there yourself. If the program indeed had spaces in the buffer it was because the buffer somehow already contained spaces by chance.

    You can use std::istream::gcount() to determine how many characters were read.