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In computer programming, conditional compilation is a compilation technique which results in differring executable programs depending on parameters specified. This technique is commonly used when these differences in the program are needed to run it on different platforms, or with different versions of required libraries or hardware.
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.
An alternative in both C and C++, especially in situations in which a pointer to the number is required, is to apply the const qualifier to a global variable. This causes the value to be stored in memory, instead of being substituted by the preprocessor. However, in modern C++ code, the constexpr keyword, introduced in C++11, is used instead:
Translation units define a scope, roughly file scope, and functioning similarly to module scope; in C terminology this is referred to as internal linkage, which is one of the two forms of linkage in C. Names (functions and variables) declared outside of a function block may be visible either only within a given translation unit, in which case they are said to have internal linkage – they are ...
If-then-else flow diagram A nested if–then–else flow diagram. In computer science, conditionals (that is, conditional statements, conditional expressions and conditional constructs) are programming language constructs that perform different computations or actions or return different values depending on the value of a Boolean expression, called a condition.
C++ began as a fork of an early, pre-standardized C, and was designed to be mostly source-and-link compatible with C compilers of the time. [1] [2] Due to this, development tools for the two languages (such as IDEs and compilers) are often integrated into a single product, with the programmer able to specify C or C++ as their source language.
The C preprocessor (used with C, C++ and in other contexts) defines an include directive as a line that starts #include and is followed by a file specification. COBOL defines an include directive indicated by copy in order to include a copybook. Generally, for C/C++ the include directive is used to include a header file, but can
Compiler files (such as C headers) may have different names. Shared libraries may be compiled and installed in different ways. One way to handle platform differences is to write conditionally compiled code (i.e. via #ifdef), but because of the wide variety of build environments, this approach quickly becomes unmanageable. Autotools is designed ...