对于全局的变量

如果内置类型的变量未被显示地初始化，它的值将由定义的位置决定。

(1).定义在函数体之外的变量将被初始化为0；

(2).定义在函数体内部的变量将不被初始化，它的值将是任意的。

 

对于(1)举例如下：

short sn;int in;long ln;long long lln;float f;double d;long double ld;bool b;char c;wchar_t wc;int nArr[10];void PrintVariable() {	cout << "short:" << sn << endl;	cout << "int:" << in << endl;	cout << "long:" << ln << endl;	cout << "long long:" << lln << endl;	cout << "float:" << f << endl;	cout << "double:" << d << endl;	cout << "long double:" << ld << endl;	cout << "bool:" << "he" << c << "llo" << endl;	cout << "char:" << c << endl;	cout << "wchar_t：" << "he" << wc << "llo" << endl;	cout << "print array:" << endl;	for (int i = 0; i < 10; i ++)	{		cout << nArr[i] << "    ";	}	cout << endl;}

结果

short:0

int:0long:0long long:0float:0double:0long double:0bool:he llochar: wchar_t:he0lloprint array:0    0    0    0    0    0    0    0    0    0 

对于(1)举例如下：

void PrintVariable() {	short sn;	int in;	int nArr[10];	int num = in;					//未被初始化，不请允许拷贝：Run-Time Check Failure #3 - The variable 'in' is being used without being initialized.	cout << "short:" << sn << endl;			//未被初始化,不允许访问该成员：Run-Time Check Failure #3 - The variable 'sn' is being used without being initialized.	cout << nArr[0] << in << endl;			//未被初始化,不允许访问该成员：Run-Time Check Failure #3 - The variable 'in' is being used without being initialized.}

 

类内的成员变量

如果是在类中定义的类成员，则初始化的顺序为：

1.构造函数初始化

2.如果没有构造函数，则通过类内的初始值进行初始化(可能有些较老的版本不允许有类内初始值)

3.默认初始化(值将是未定义的，是任意的)

没有构造函数初始化：

#pragma once#include 
    
     using namespace std;class TestData{public:	//TestData(void);	~TestData(void);	void PrintVariable() 	{		cout << "short:" << sn << endl;		cout << "int:" << in << endl;		cout << "long:" << ln << endl;		cout << "long long:" << lln << endl;		cout << "float:" << f << endl;		cout << "double:" << d << endl;		cout << "long double:" << ld << endl;		cout << "bool:" << "he" << c << "llo" << endl;		cout << "char:" << c << endl;		cout << "wchar_t：" << "he" << wc << "llo" << endl;		cout << "print array:" << endl;		for (int i = 0; i < 10; i ++)		{			cout << nArr[i] << "    ";		}		cout << endl;	}private:	short sn;	int in;	long ln;	long long lln;	float f;	double d;	long double ld;	bool b;	char c;	wchar_t wc;	int nArr[10];};
    

结果(很可怕)：

short:-13108

int:-858993460long:-858993460long long:-3689348814741910324float:-1.07374e+008double:-9.25596e+061long double:-9.25596e+061bool:he蘬lochar:wchar_t：he52428lloprint array:-858993460    -858993460    -858993460    -858993460    -858993460    -858993460    -858993460    -858993460    -858993460    -858993460

通过构造函数初始化

#pragma once#include 
    
     using namespace std;class TestData{public:	TestData(void) : sn(0), in(0), ln(0), lln(0), f(0), d(0.0), ld(0), b(true), c(' '), wc(L' ')	{		memset(nArr, 0, 10*sizeof(int));	}	~TestData(void);	void PrintVariable() 	{		cout << "short:" << sn << endl;		cout << "int:" << in << endl;		cout << "long:" << ln << endl;		cout << "long long:" << lln << endl;		cout << "float:" << f << endl;		cout << "double:" << d << endl;		cout << "long double:" << ld << endl;		cout << "bool:" << "he" << c << "llo" << endl;		cout << "char:" << c << endl;		cout << "wchar_t：" << "he" << wc << "llo" << endl;		cout << "print array:" << endl;		for (int i = 0; i < 10; i ++)		{			cout << nArr[i] << "    ";		}		cout << endl;	}private:	short sn;	int in;	long ln;	long long lln;	float f;	double d;	long double ld;	bool b;	char c;	wchar_t wc;	int nArr[10];};
    

结果：

short:0

int:0long:0long long:0float:0double:0long double:0bool:he llochar:wchar_t：he32lloprint array:0    0    0    0    0    0    0    0    0    0