c extern

1. Basic explanation Extern can be placed before a variable or function to indicate that the definition of a variable or function is in another file, prompting the compiler to find its definition in other modules when it encounters this variable or function. In addition, extern can be used to specify links. 2 problem: extern variable An array is define

The role of extern "c" and the role of extern Function: Mixed Programming of C and C ++. Principle: After the C and C ++ compilers compile, the function name will be compiled into different names. The target cannot be found in the Link stage name search, which will be explained in the following examples. Usage: ①. Function defined in file c ,. when the cpp file is to be called. use

When reading svm. h, we found the following code: #ifndef _LIBSVM_H#define _LIBSVM_H#define LIBSVM_VERSION 317#ifdef __cplusplusextern "C" {#endifApparently, the first three lines of code are intended to prevent repeated references to header files. What do 5-6 lines mean? An enterprise once gave the following interview question: why do standard header files have a structure similar to the following? #ifndef __INCvxWorksh#define __INCvxWorksh #ifdef __cplusplusextern "C" {#endif /*...*/ #ifdef

, its survival time is changed. After changing a global variable to a static variable, it changes its scope and limits its scope of use. What is the difference between a static function and a common function? Only functions used in the current source file should be declared as internal functions (static). Internal functions should be described and defined in the current source file. For functions that can be used outside the current source file, it should be described in a header file that the

1. Basic explanationExtern can be placed before a variable or function to indicate that the definition of a variable or function is in another file, prompting the compiler to find its definition in other modules when it encounters this variable or function.In addition, extern can be used to specify links.　　2 problem: extern variableAn array is defined in a source file:

Example:Two files:C file: C. c **************************************** ******* Int external = 5; // global variable. The default value is extern.Int func () // global function. The default value is extern.{Return external;} **************************************** ******* Cpp file: CPP. cpp **************************************** ******* # Include "iostream"Using namespace std; # Ifdef _ cplusplusExtern "C"{# EndifExtern int external; // tell

Static is a commonly used modifier in C + +, which is used to control the storage and visibility of variables. extern, "C" is a means to enable C + + to invoke C writing library files, if you want to prompt the compiler to use C to handle functions, then use extern "C" to explain. The static keyword in a. C language In the C language, static can be used to modify local variables, global variables, and funct

Recently learning Lua, about LUA compiled place, because Lua is written in C, C language in C + + functions, need to use the extern "C" compile before, seemingly did not touch this knowledge, write a blog to commemorate, by the way the role of the extern keyword.I. The role of extern "C"This is the first time I've seen it, because I've never had C + + to callC's

The use of extern and static in C ++ is confusing. The following is a summary: 1. the global variable definition is used to modify the global variable definition. The global variable definition is used to expand the scope of the global variable, other files can also use this global variable static to modify the definition of the global variable to limit that this global variable can only be used in this file. after the CPP file is compiled, it becomes

Extern "C" contains a double meaning, which can be obtained literally: first, the target is "extern", and second, the target is "C.First, let's take a look.:A. in a file, if an external variable is not defined at the beginning of the file, its valid range is limited to the end of the definition. If you need to reference this variable before the definition, you need to use the keyword "

connect to them, you will find a very cute error.The solution is to specify it as a C function:Extern "C" Function DescriptionIf you specify a group of functions:Extern "C "{N function descriptions}If you want to mix C and C ++:# Ifdef _ cplusplusExtern "C "{# EndifN function descriptions# Ifdef _ cplusplus}# Endif Extern "C" indicates that the internal Symbol names generated by Compilation Use the c Convention. C ++ supports function overloading, bu

and type information, C + + is this mechanism to implement function overloading. Here's an example of how to use C's function in C + +,Or, you use C + + functions in C.Examples of C + + reference functionsTEST.c#include void MyTest (){printf ("MyTest in. c file ok\n");}Main.cppextern "C"{void MyTest ();}int main (){MyTest ();return 0;}To reference C + + functions in CIn C, when referencing functions and variables in the C + + language, a C + + function or variable is declared in the

The C language often appears in the file duplicate contains and causes the global variable to duplicate the definition, below an example illustrates -----Makefile CC = gcc objs = main.o errhandle.o strcopy.o cflags =-wall-std=c99 main: ${objs} # or $ (OBJS), ${OBJS} i s shell style ${cc} ${cflags}-o $@ ${objs} main.o:main.c errhandle.h strcopy.h ${cc} ${cflags}-C main.c errhandle.o:errhandle.c errhandle.h ${CC} ${cflags}-C errhandle.c strcopy.o:strcopy.c strcopy.h Errhandle.h ${CC} ${

The intent of extern "C" in C + + is to implement mixed programming between C + + and C and other languages.C + + supports function overloading, whereas programming language C is not supported. Functions are compiled in C + + with different names in the symbol library than in the C language.For example, suppose a function is prototyped as: void int int y) The function is compiled by the C compiler and is named _foo in the symbol library.The C+ + compi

In the C language, the modifier extern is used before the declaration of a variable or function to illustrate that "this variable/function is defined elsewhere and is referenced here." 1. Declarations of extern-modified variables. For example, if the file a.c needs to refer to the variable int v in B.C, you can declare the extern int v in A.C, and then you can r

STACK.O, which contains the. Data segment of variables A and Stack,main also incorporates the. Data segment of the MAIN.O and STACK.O, which contains the variables B and top,main. Text segment merges MAIN.O and S TACK.O. Text segment that contains the definitions of each function. As shown in the following:If you put STACK.O in front of MAIN.O at compile time, that is: gcc stack.o main.o-o Main, the executable file from the MAIN.O variable or function in each paragraph of main is discharged to