define once more

1. #pragma once is used to prevent a head file from being include multiple times; #ifndef, #define, #endif用来防止某个宏被多次定义. 2. #pragma once is compile-related, which means it can be used on the compilation system, but not necessarily in other compiling

1. Define (that is, host variable)The main role of the host variable is to act as an alternative variable, a medium in which the host environment can interact with Oracle . When you define a host variable by define, you must specify the variable

There are many places in the C language where macro definitions are used, such as in header files to prevent header files from being repeatedly included: #ifndef ctest_header_h #define CTEST_HEADER_H /header file content #endif Many macro

Let's look at a few examples (1) struct{int x; int y;} Test1; Well, define the structure test1, test1.x and test1.y can be used in the statement. (2) struct test {int x; int y;} Test1; Well, define the structure test1, test1.x and test1.y can be

: This article mainly introduces the difference between const and define in php (supplement). If you are interested in PHP tutorials, refer to it. A constant is the identifier (name) of a simple value ). As its name implies, this value cannot be

# Pragma once is guaranteed by the compiler: the same file will not be contained multiple times. Note that the "same file" here refers to a physical file, not two files with the same content. The advantage is that you don't have to think about a

A constant is an identifier (first name) of a simple value. As the name implies, the value cannot be changed during script execution (except for the so-called magic constants, they are not constants). Changshime is considered to be case sensitive.

1, define--(no parameter macro definition)Usage: The general form is: #define Identifier string(1) "#" means that it is a pre-processing command, usually "#" is the pre-processing command;"Define" defines the command for the macro; "identifier" is

1.1. # define variant, that is, # ifndef, can prevent repeated references to header files# Ifdef and # define combinations are generally used in header files to prevent repeated references of multiple files to the same header file.In actual use,

Resolution # pragma command Among all the pre-processing commands, the # pragma command may be the most complex. It is used to set the compiler status or to instruct the compiler to complete some specific actions. # The Pragma command provides a