In all preprocessing instructions, the # prgMA instruction may be the most complicated, its role is to set the status of the compiler or indicate that the compiler does some specific actions. #pragma instructions give each compiler a method to give the host or operating system proprietary feature in the case where the C and C language is fully compatible. Based on definitions, compilation indication is perfect for machines or operating systems and is different for each compiler.
Its format is generally: #pragma para
Where parameters are parameters, look at some common parameters.
(1) Message parameters. The Message parameter is my favorite parameter, which can be compiled in the information output window
The corresponding information is output, which is very important for the control of source code information. The method of use is:
#Pragma message ("Message Text")
When the compiler encounters this instruction, print the message text in the compilation output window.
When we define many macros in the program to control the source code version, we may have forgotten that there is no correct settings. At this time we can use this instruction to check when compiling. Suppose we want to determine if you have anywhere in the source code _X86 this macro can be used in the following method
#ifdef _x86
#Pragma message ("_ x86 macro actid!")
#ENDIF
When we define the _x86 this macro, the application will display in the compile output window when compiling "_
X86 Macro Activated! ". We will not scratch it because some specific macro they define.
.
(2) Another multi-use PRAGMA parameter is Code_SEG. Formats such as:
#pragma code_seg ([Section-Name "[," Section-Class "]])
It can set the code segment stored in the program in the program, which will be used when we develop the driver.
(3) #pragma ONCE (more common)
As long as the first instructions in the header file can guarantee that the header file is compiled once, this instruction is actually in VC6, but considers compatibility and not much using it.
(4) #pragma HDRSTOP indicates that the pre-translated header files will be, and the header files will not be precompiled. The BCB can pre-translate the header file to speed up the speed of the link, but if all header files are pre-compiled, it may account for too much disk space, so use this option to exclude some header files.
There is a dependency between the units, such as unit A dependent unit B, so unit B is compiled by unit A. You can use #pragma startup to specify compilation priority, if #pragma package (smart_init) is used, BCB will compile according to the size of the priority.
(5) #pragma resource "* .dfm" means adding resources in the * .dfm file to the project. * .dfm includes a form
Definition of appearance.
(6) #pragma Warning (Disable: 4507 34; Once: 4385; Error: 164)
Equivalent to:
#pragma Warning (Disable: 4507 34) // Does not display 4507 and 34 warning information
#pragma Warning (ONCE: 4385) // 4385 Warning information only reports once
#pragma Warning (Error: 164) // Put the 164 warning message as an error.
At the same time, this Pragma Warning also supports the following format:
#pragma Warning (push [, n])
#pragma Warning (POP)
Here n represents a warning level (1 --- 4).
#pragma Warning (Push) Save existing warning status of all warning information.
#pragma warning (push, n) Save existing warning status of all warning information, and set the global warning level to n.
#pragma Warning (POP) pops up the last warning message in the stack, in the stack and out of the stack
Everything is canceled. E.g:
#pragma Warning (Push)
#pragma Warning (Disable: 4705)
#pragma Warning (Disable: 4706)
#pragma Warning (Disable: 4707)
// .......
#pragma Warning (POP)
At the end of this code, re-save all warning information (including 4705, 4706, and 4707).
(7) Pragma Comment (...)
This instruction puts a comment record into an object file or executable.
Commonly used lib keywords can help us connect into a library file.
