In this post we will explore what I consider the most significant language change in C++17. I call it the most significant because it changes the way you design your resource-managing types and how you think about initialization. It is often called “guaranteed copy elision”, but I will not use that name (except for this single time) because it does not reflect what this feature is. C++ has completely changed the meaning of rvalue (actually, prvalue). Continue reading
In this short post I wanted to share links to three online services that I use for testing different aspects of C++ and C++ compilers.
- https://wandbox.org/ — this allows you to compile and observe the output of programs compiled in different versions of GCC and Clang, with different versions of Boost libraries;
- https://godbolt.org/ — this allows you to see the assembly of C++ programs generated with different compilers on different platforms;
- http://quick-bench.com/ — this allows you to micro-benchmark C++ functions on different versions of GCC and Clang using Google’s benchmark library.
Let’s start with the problem. I want to check whether a program received a text message that consists of four consecutive zeroes. Not
'0', but the numeric zero. I will create a constant
std::string representing the special sequence and compare the messages (also stored as
std::strings) I receive. I cannot just type:
const std::string Special = "\0\0\0\0";
As this would be interpreted, according to C rules, as a zero-length string. But there is another constructor exactly for our case, where I can say “character
C repeated N times”. So, I type:
const std::string Special ('\0', size_t(4));
I could have used braces for the initialization, but since I am aware of the
std::initializer_list gotchas (like the one described here), I am following my rule of thumb, “if you suspect the type might expose an initializer-list constructor, and you want to initialize through a different constructor, do not use braces”.
Now I can test my program. It still doesn’t work correctly for some reasons. It does not recognize the special messages as special, even though I would expect it to. I test and debug it for quite some time, until finally do I realize that my string
Special has a different value than I think. Continue reading
Compiler warnings are a very useful tool for detecting bugs in your program. Because you can enable them selectively, and because you can choose to turn them into hard errors on your compiler, you can in fact build a dialect, which is a safer subset of C++. You can enable even more warning if you assist your compiler a bit and instruct it about your intentions. We will see how to do it in one case. Continue reading