The True Cost of Calls

The cost of virtual functions is often invoked as a reason to C++’s poor performance compared to other languages, especially C. This is an enduring myth that, like most myths, have always bugged me. C++ myths are propagated by individuals that did not know C++ very well, tried it one weekend in 1996, used a bad compiler, knew nothing about optimization switches, and peremptorily declared C++ as fundamentally broken. Well, I must agree that C++ compilers in the mid-90s weren’t all that hot, but in the last fifteen years, a lot have been done. Compilers are now rather good at generating efficient C++ code.

However, the cost of calls, whether or not they are virtual, is not dominated by the the call itself (getting the address to jump to and jumping) but by everything else surrounding the call, like the stack setup and argument passing. Let us debunk that myth by looking at what types of calls are available in C and C++, how they translate to machine code, and see how faster or slower they are relative to each other.

Safer Integer Constants (Part II)

In C and C++, the behavior of integer promotions is not the same whether we use signed integers or unsigned integers. In bit twiddling hacks, it is not immediately apparent that it is a problem that may lead to unexpected result whenever code is ported to a different architecture. This is a recurring topic whenever I discuss portability with friends. Very often, they argue that if it works on Windows and 32 bits x86 Linux, that’s pretty much all there is to it.

Of course, I couldn’t disagree more. I have learned the hard way.

Safer Float Types

This week, we’ll be following last week’s post, where we looked at type-safe integer constants, with floating point constants, that is, float and double.

Safer Integer Constants

Consider the following short C (or C++) program:

const int thingy=123123123123;

Depending on your compiler, the above code may succeed, fail, produce a warning, or be accepted quietly and result in undefined behavior, which is extremely bad.

The Right Tool

On his blog, Occasionally Sane, my friend Gnuvince tries to make a case for Python as a first programming language. He presents Python with a series of bullets, each giving a reason why Python is a good choice. While I think it may be a good choice pedagogically, it may not be a good pragmatic choice when someone is learning a programming language to find a job, as one of his reader commented.

But I think that betting on a sole language to base a programming career on is about as silly as someone mastering only the hammer looking for a construction job. His limited skills might not permit him to find a job, and even if he finds one, he may be confined to menial, unchallenging tasks. To push the tool analogy further, another workman that masters a wide array of tools will probably be more solicited and appreciated in his work-group, and be lead to more and more complex tasks, and more responsibilities within his group. Programming is very much the same: sometimes, it just takes something else than a hammer, and the right guy for the job is the guy that has the largest toolbox—the one with the Torx screwdriver set.