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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]
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.
In general, a translation unit shall contain no more than one definition of any class type. In this example, two definitions of the class type C occur in the same translation unit. This typically occurs if a header file is included twice by the same source file without appropriate header guards.
The first C Standard specified that __STDC__ expand to "1" if the implementation conforms to the ISO standard and "0" otherwise and that __STDC_VERSION__ expand to a numeric literal specifying the version of the standard supported by the implementation. Standard C++ compilers support the __cplusplus macro. Compilers running in non-standard mode ...
Using #pragma once allows the C preprocessor to include a header file when it is needed and to ignore an #include directive otherwise. This has the effect of altering the behavior of the C preprocessor itself, and allows programmers to express file dependencies in a simple fashion, obviating the need for manual management.
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.
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.
In contrast to other languages, in Smalltalk the conditional statement is not a language construct but defined in the class Boolean as an abstract method that takes two parameters, both closures. Boolean has two subclasses, True and False, which both define the method, True executing the first closure only, False executing the second closure ...