Search results
Results from the WOW.Com Content Network
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.
The Watcom C/C++ compiler also uses the #pragma aux [20] directive that allows the user to specify their own calling convention. As its manual states, "Very few users are likely to need this method, but if it is needed, it can be a lifesaver".
In computer programming, a directive or pragma (from "pragmatic") is a language construct that specifies how a compiler (or other translator) should process its input. Depending on the programming language , directives may or may not be part of the grammar of the language and may vary from compiler to compiler.
The #pragma pack directive can only be used to reduce the packing size of a structure from the project default packing. [11] This leads to interoperability problems with library headers which use, for example, #pragma pack(8), if the project packing is smaller than this.
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.
A common vendor pragma with a similar functionality in C is #pragma once. C++ as of C++20 has the import and module directives for modules. [15] [16] These directives are the only ones that do not start with a # character; instead, they start with import and module respectively, optionally preceded by export.
C++ has more complicated rules about pointer assignments that add qualifiers as it allows the assignment of int ** to const int *const * but not the unsafe assignment to const int ** while C allows neither of those (although compilers will usually only emit a warning). C++ changes some C standard library functions to add additional overloaded ...
In computer programming, a precompiled header (PCH) is a (C or C++) header file that is compiled into an intermediate form that is faster to process for the compiler.Usage of precompiled headers may significantly reduce compilation time, especially when applied to large header files, header files that include many other header files, or header files that are included in many translation units.