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Macros in makefiles may be overridden in the command-line arguments passed to the Make utility. Environment variables are also available as macros. For example, the macro CC is frequently used in makefiles to refer to the location of a C compiler. If used consistently throughout the makefile, then the compiler used can be changed by changing ...
For #include guards to work properly, each guard must test and conditionally set a different preprocessor macro. Therefore, a project using #include guards must work out a coherent naming scheme for its include guards, and make sure its scheme doesn't conflict with that of any third-party headers it uses, or with the names of any globally visible macros.
The C++ Standard Library provides several generic containers, functions to use and manipulate these containers, function objects, generic strings and streams (including interactive and file I/O), support for some language features, and functions for common tasks such as finding the square root of a number.
Both tools were working examples of a build tool that supported both Unix and Windows, but they suffered from a serious flaw: they required Windows developers to use the command line even though many prefer to use an integrated development environment (IDE) such as Visual Studio.
Similarly, a variable CPPFLAGS exists with switches to be passed to the C or C++ preprocessor. Similarly, FFLAGS enables the addition of switches for a Fortran compiler. These variables are most commonly used to specify optimization or debugging switches to a compiler, as for example -g, -O2 or (GCC-specific) -march=athlon.
For example, given int i = 1; j = 2;, the result of max(i,j) is 2. If a and b were only evaluated once, the result of max(i++,j++) would be the same, but with double evaluation the result is 3. Hidden order of operation. Failure to bracket arguments can lead to unexpected results. For example, a macro to double a value might be written as:
The C standard library is declared as a collection of header files. The C++ standard library is similar, but the declarations may be provided by the compiler without reading an actual file. C standard header files are named with a .h file name extension, as in #include <stdio.h>. Typically, custom C header files have the same extension.
Automake is written in Perl and must be used with GNU Autoconf. [2] Automake contains the following commands: aclocal; automake; aclocal, however, is a general-purpose program that can be useful to autoconf users. The GNU Compiler Collection (GCC), for example, uses aclocal even though its makefile is hand written.