Declared as a global variable

Declare as a global variable
C++ Global variables should be defined in .cpp The document defines , Not in .h In file Definition , When it's defined , Can be in .h Use... In documents extern Keyword to declare . If in .h As defined in the document , Multi tier inclusion may cause repeated definition errors . Here's an example ：

stay g_bash.cpp Define global variables in ：
// g_bash.cpp
#include “g_base.h”
int g_TicketCount = 0; // Define global variables and initialize
stay g_bash.h Use... In documents extern Keyword to declare ：

// g_bash.h
#ifndef G_BASE_H
#define G_BASE_H
extern int g_TicketCount; // Global variable declaration
#endif // G_BASE_H
Then when other files want to use these variables , as long as #include "g_base.h" That's all right. , And it will not cause repeated definition errors .main.cpp The following is an example ：

#include
#include
#include g_base.h

extern int g_TicketCount; // Global variable declaration
using namespace std;
void proc()
{
cout<< proc(): <<endl;
g_TicketCount++;
}
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
cout<< g_TicketCount = << g_TicketCount << endl;
proc();
cout<< g_TicketCount = << g_TicketCount << endl;
return a.exec();
}

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