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[2] [3] [4] When conditional compilation is done via a preprocessor that does not guarantee syntactically correct output in the source language, such as the C preprocessor, this may lead to hard-to-debug compilation errors, [5] [6] [7] which is sometimes called "#ifdef hell." [8] [9]
A newer language construct (since C++11 and C23), constexpr allows for declaring a compile-time constant value that need not consume runtime memory. [20] Inline function. For a long time, a function-like macro was the only way to define function-like behavior that did not incur runtime function call overhead.
The #ifeq function selects one of two alternatives based on whether two test strings are equal to each other. {{#ifeq: string 1 | string 2 | value if equal | value if not equal}} If both strings are valid numerical values, they are compared as numbers, rather than as literal strings: {{#ifeq: 01 | 1 | equal | not equal }} → equal
The curiously recurring template pattern (CRTP) is an idiom, originally in C++, in which a class X derives from a class template instantiation using X itself as a template argument. [1] More generally it is known as F-bound polymorphism , and it is a form of F -bounded quantification .
[1] [2] All functions use floating-point numbers in one manner or another. Different C standards provide different, albeit backwards-compatible, sets of functions. Most of these functions are also available in the C++ standard library, though in different headers (the C headers are included as well, but only as a deprecated compatibility feature).
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.
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.
It originally comes from CPL, in which equivalent syntax for e 1 ? e 2 : e 3 was e 1 → e 2, e 3. [1] [2] Although many ternary operators are possible, the conditional operator is so common, and other ternary operators so rare, that the conditional operator is commonly referred to as the ternary operator.