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I'm writing some c++ code that makes use of std::string.
I wanted to see how to code is written, so I went into the source code. (ctrl + left click).
I noticed, that there are macros everywhere.
The code even ends with:
_STD_END
// Corresponds to: #define _STD_END }
I get why macros are useful, and I use them for my own Log.hpp file, but I don't understand why anyone would use macros such as _STD_END instead of just writing }.
Just to clear up, my question is why he author of std::string, P.J. Plauger, decided to use macros in this way, and if I also should?
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We can create two or more than two strings in macro, then simply write them one after another to convert them into a concatenated string. The syntax is like below: #define STR1 "str1" #define STR2 " str2" #define STR3 STR1 STR2 //it will concatenate str1 and str2.
std::string class in C++ C++ has in its definition a way to represent a sequence of characters as an object of the class. This class is called std:: string. String class stores the characters as a sequence of bytes with the functionality of allowing access to the single-byte character.
__cplusplus. This macro is defined when the C++ compiler is in use. You can use __cplusplus to test whether a header is compiled by a C compiler or a C++ compiler. This macro is similar to __STDC_VERSION__ , in that it expands to a version number.
__LINE__ is a preprocessor macro that expands to current line number in the source file, as an integer. __LINE__ is useful when generating log statements, error messages intended for programmers, when throwing exceptions, or when writing debugging code.
That’s the Dinkumware library, which Microsoft licenses (although they've recently taken over full maintenance of their version). The _STD_BEGIN and _STD_END macros are used for customizing the std namespace. Some compilers don't (didn't?) support namespaces; for those compilers, the macro expansions are empty. Some compilers need some indirection, and those macros expand into directives that put the code into an implementor-specific namespace (i.e., a namespace whose name begins with an underscore followed by a capital letter), which may or may not be complemented by a using-directive to pull the contents of that namespace into std. And in many cases they expand into the obvious, ordinary namespace std { and }, respectively.
In short, they're about configurability for a multi-platform library implementation.
I worked for Dinkumware for quite a few years, so I have first-hand knowledge.
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