c++奇怪的搞法汇总

最新推荐文章于 2023-05-04 13:33:31 发布

原创最新推荐文章于 2023-05-04 13:33:31 发布 · 830 阅读

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本文探讨了C++中静态局部变量的应用、预编译宏定义的使用限制、安全删除内存的方法、成员变量初始化的问题以及类型转换的实践案例。通过具体代码示例介绍了如何正确地运用这些特性。

1 静态局部变量

int WorkEvent::GenerateId()

{
static int uiEventId = 0;
return uiEventId++;

}

2 define and enum 预编译是顺序的，不能随便调整

#define MAKE_UNION(VAR) VAR
#define MAKE_STRINGS(VAR) #VAR

#define APP_EVENT_TYPE(DO) DO(DIGIT), DO(DIGIT2)

typedef enum
{
APP_EVENT_TYPE(MAKE_UNION)
}APP_EVENT_NAME;

const string g_strAryAppEventName[EVENT_NAME_END+1] =
{
APP_EVENT_TYPE(MAKE_STRINGS)
};

3 delete

#define SAFE_DELETE(p) {if(NULL != p) {delete p; p = NULL;}}
#define SAFE_DELETE_ARRAY(p) {if(NULL != p) {delete [] p; p = NULL;}}

down vote favorite

Before C++11, we could only perform in-class initialization on static const members of integral or enumeration type.Stroustrup discusses this in his C++ FAQ, giving the following example:

class Y {
  const int c3 = 7;           // error: not static
  static int c4 = 7;          // error: not const
  static const float c5 = 7;  // error: not integral
};

5 类型转化

#include <string>
#include <iostream>
#include <sstream>

int main(void) {
std::string str;
std::stringstream stream;
stream<<"1"<<2;
stream>>str;

std::cout<<str<<std::endl;

return 0;
}

6 string *ptString1 = false;

    //string *ptString1=true; compile error

    string *ptString1 = false;
   if (!ptString1) {
       cout << "true1" << endl;
   }

   string *ptString2 = NULL;
   if (!ptString2) {
       cout << "true2" << endl;
   }

   string *ptString3 = new string;
   if (ptString3) {
       cout << "true3" << endl;
   }

   int x = 0;
   if (!x) {
       cout << "true4" << endl;
   }

   int y = 1;
   if (y) {
       cout << "true5" << endl;
   }

java all compile error