Question

Based on Mats Petersson’s results, I did some tests. My work on turning the assert on and off by defining a macro is not necessary. My conclusions are:

1. Including standard headers such as <cassert>, <vector>, <memory> and so on, takes little compilation time. We don’t need to care.
2. Be careful in including your own files. Include those that are really needed because the dependent requires recompilation after the change of the depended.
3. Be careful when including collection headers of class library, such as <QWidgets> (Qt header to include all its widgets). This takes a huge time in compilation.

[Original Post]

Does it take long compilation time if every files includes “assert.h”? I think similar questions on “math.h” or other common files. I don’t like pre-compiled header. This happens when I have a Vector3D class which represents a vector in 3D space with x, y, z component. The class is used almost everywhere. I have a function named component(int i) where i is asserted between 0 and 2. For performance reason, I don’t put its implementation in cpp file. Thus “assert.h” is included almost everywhere.

#pragma once

#include <assert.h>

/// A vector in a 3D space with 3 components: x, y, and z.
class Vector3D
{
public:
    Vector3D(float x = 0, float y = 0, float z = 0)
    {
        m_component[0] = x;
        m_component[1] = y;
        m_component[2] = z;
    }

    float x() const    {return m_component[0];}
    float y() const    {return m_component[1];}
    float z() const    {return m_component[2];}

    void setX(float x)    {m_component[0] = x;}
    void setY(float y)    {m_component[1] = y;}
    void setZ(float z)    {m_component[2] = z;}

    float component(int i) const
    {
        assert(i >= 0 && i < 3);
        return m_component[i];
    }

    float& component(int i)
    {
        assert(i >= 0 && i < 3);
        return m_component[i];
    }

private:
    float m_component[3];
};

Inspired by Floris Velleman, I add a file to define my ASSERT to turn on and off it. It requires changing assert to ASSERT in the code using assert. Thanks.

#ifdef USE_ASSERT
# include <assert.h>
# define ASSERT(statement) assert(statement)
#else
# define ASSERT(statement)
#endif

Answer 1

All headers use the same inclusion model, which is tremendously slow. Some headers may be more complex than others, but in general, you don’t include a header you don’t need.