What is #pragma directive?

The #pragma preprocessor directive allows each compiler implementation to implement compiler-specific features. Each implementation of C and C++ supports some features unique to its host machine or operating system. Some programs, for instance, need to exercise precise control over the memory areas where data is placed or to control the way certain functions receive parameters. The #pragma directives offer a way for each compiler to offer machine- and operating system-specific features while retaining overall compatibility with the C and C++ languages. Pragmas are machine- or operating system-specific by definition, and are usually different for every compiler.