GLSL Shader Program Randomly Fails to Compile - c++

Question

I'm experiencing a strange behaviour in my OpenGL application. I generate a number of GLSL programs during the initialization of the program. The shader programs are read from text files and the programs are compiled and linked. However, I randomly encounter compilation errors for one of the shader programs (a pass-through vertex shader). I cannot understand why the program loads perfectly fine and the shader program successfully compiles several times but fails to do in other times!
Here is the shader code:
#version 330
// vertex position in the model space
layout(location = 0) in vec3 inPosition;
layout(location = 1) in vec2 inTexCoord;
// will be interporlated for each fragment
smooth out vec2 vTexCoord;
// uniforms
uniform mat4 projectionMatrix;
uniform mat4 modelViewMatrix;
void main(void) {
gl_Position = projectionMatrix * modelViewMatrix * vec4(inPosition, 1.0);
vTexCoord = inTexCoord;
}
And here is the code for compiling the shader (passThroughVertShader is a QString):
this->passThroughVertShader = glCreateShader(GL_VERTEX_SHADER);
const char *passThroughVertShaderCodeC = passThroughVertShaderCode.toStdString().c_str();
sourceCode = passThroughVertShaderCodeC;
glShaderSource(this->passThroughVertShader, 1, &sourceCode, NULL);
glCompileShader(this->passThroughVertShader);
glGetShaderiv(this->passThroughVertShader, GL_COMPILE_STATUS, &isCompiled);
if(isCompiled == GL_FALSE)
{
qDebug("ERROR compiling pass-through vertex shader..");
exit(-1);
}
glAttachShader(this->shaderProgram, this->passThroughVertShader);
And the function that loads it:
QString MyClass::readShaderFile(const QString &filename) {
QString content;
QFile file(filename);
if (file.open(QIODevice::ReadOnly)) {
QTextStream tStream(&file);
content = tStream.readAll();
}
return content;
}
Update:
Following Andon's suggestion, I double checked and I wasn't checking the log after failure. Here is what the log says:
Error: 0(17) : error C0000: syntax error, unexpected '!', expecting "::" at token "!"

Answer 1

Ok, answering myself here. Thanks to AndonM.Coleman for pointing out that I should check the error log. The output was not clear, but it lead me to another SO question that shed some light on a bug I had in the code. Apparently I was doing the right thing for compiling all other shaders in the program and somehow forgot one line when I was writing the code for this one. What I should have been doing was the following:
string passThroughVertShaderCodeS = passThroughVertShaderCode.toStdString();
const char *passThroughVertShaderCodeC = passThroughVertShaderCodeS.c_str();
In short, the toStdString() method was returning a temporary copy of the buffer. Since I'm calling c_str() on that temporary copy which gets destroyed after that line, that pointer becomes invalid. I'm not sure why it occasionally succeeded though.