What is a pragma?

This is a preprocessor directive that can be used to turn on or off certain features. It is of two types #pragma startup, #pragma exit and pragma warn. pragma startup allows us to specify functions called upon program startup. pragma exit allows us to specify functions called upon program exit. pragma warn tells the computer to suppress any warning or not. many other #pragma style that can use to control compiler read less

The ‘#pragma’ directive is the method specified by the C standard for providing additional information to the compiler, beyond what is conveyed in the language itself. Three forms of this directive (commonly known as pragmas) are specified by the 1999 C standard. A C compiler is free to attach any meaning it likes to other pragmas. Its syntax is _Pragma (string-literal), where string-literal can be either a normal or wide-character string literal. It is destringized, by replacing all ‘\\’ with a single ‘\’ and all ‘\"’ with a ‘"’. The result is then processed as if it had appeared as the right hand side of a ‘#pragma’ directive. For example, _Pragma ("GCC dependency \"parse.y\"") has the same effect as #pragma GCC dependency "parse.y". The same effect could be achieved using macros, for example #define DO_PRAGMA(x) _Pragma (#x) DO_PRAGMA (GCC dependency "parse.y") read less

Pragmatic is a very complex pre processor directive as it depends on the platform/hardware. It is used to indicate the minimum memory size to be used for any data type to increase the speed of data access. We know that a character is of size one byte but when you declare #pragma 4 , every character will occupy 4 bytes of memory, this will speed up your system because if you're writing code for 32 bit cpu, which indicates that it's data bus size is 32 bits meaning it can fetch 4 bytes of data in one cpu cycle then it would be efficient to declare variable of size which is multiple of 4. There's another cover you need to know odd address and even address. Let me know in comments if you want me to explain that. read less

#pragma preprocessor directive allows each compiler to implement compiler-specific features that can be turned on and off with the #pragma statement. For instance, your compiler might support a feature called loop optimization. This feature can be invoked as a command-line option or as a #pragma directive. To implement this option using the #pragma directive, you would put the following line into your code: #pragma loop_opt(on) Conversely, you can turn off loop optimization by inserting the following line into your code: #pragma loop_opt(off) read less