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：
1short sn; 2int in; 3long ln; 4long long lln; 5float f; 6double d; 7long double ld; 8bool b; 9char c; 10wchar_t wc; 11int nArr[10]; 12 13void PrintVariable() 14{ 15 cout << "short:" << sn << endl; 16 cout << "int:" << in << endl; 17 cout << "long:" << ln << endl; 18 cout << "long long:" << lln << endl; 19 cout << "float:" << f << endl; 20 cout << "double:" << d << endl; 21 cout << "long double:" << ld << endl; 22 cout << "bool:" << "he" << c << "llo" << endl; 23 cout << "char:" << c << endl; 24 cout << "wchar_t：" << "he" << wc << "llo" << endl; 25 cout << "print array:" << endl; 26 for (int i = 0; i < 10; i ++) 27 { 28 cout << nArr[i] << " "; 29 } 30 cout << endl; 31}
结果
short:0
int:0
long:0
long long:0
float:0
double:0
long double:0
bool:he llo
char:
wchar_t:he0llo
print array:
0 0 0 0 0 0 0 0 0 0
对于(1)举例如下：
1void PrintVariable() 2{ 3 short sn; 4 int in; 5 int nArr[10]; 6 7 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. 8 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. 9 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. 10}
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：
1#pragma once 2 3#include <iostream> 4using namespace std; 5 6class TestData 7{ 8 9public: 10 //TestData(void); 11 ~TestData(void); 12 13 void PrintVariable() 14 { 15 cout << "short:" << sn << endl; 16 cout << "int:" << in << endl; 17 cout << "long:" << ln << endl; 18 cout << "long long:" << lln << endl; 19 cout << "float:" << f << endl; 20 cout << "double:" << d << endl; 21 cout << "long double:" << ld << endl; 22 cout << "bool:" << "he" << c << "llo" << endl; 23 cout << "char:" << c << endl; 24 cout << "wchar_t：" << "he" << wc << "llo" << endl; 25 cout << "print array:" << endl; 26 for (int i = 0; i < 10; i ++) 27 { 28 cout << nArr[i] << " "; 29 } 30 cout << endl; 31 } 32private: 33 short sn; 34 int in; 35 long ln; 36 long long lln; 37 float f; 38 double d; 39 long double ld; 40 bool b; 41 char c; 42 wchar_t wc; 43 int nArr[10]; 44 45};
结果(很可怕)：
short:-13108
int:-858993460
long:-858993460
long long:-3689348814741910324
float:-1.07374e+008
double:-9.25596e+061
long double:-9.25596e+061
bool:he蘬lo
char:
wchar_t：he52428llo
print array:
-858993460 -858993460 -858993460 -858993460 -858993460 -858993460
-858993460 -858993460 -858993460 -858993460
通过构造函数初始化
1#pragma once 2 3#include <iostream> 4using namespace std; 5 6class TestData 7{ 8 9public: 10 TestData(void) : sn(0), in(0), ln(0), lln(0), f(0), d(0.0), ld(0), b(true), c(' '), wc(L' ') 11 { 12 memset(nArr, 0, 10*sizeof(int)); 13 } 14 15 ~TestData(void); 16 17 void PrintVariable() 18 { 19 cout << "short:" << sn << endl; 20 cout << "int:" << in << endl; 21 cout << "long:" << ln << endl; 22 cout << "long long:" << lln << endl; 23 cout << "float:" << f << endl; 24 cout << "double:" << d << endl; 25 cout << "long double:" << ld << endl; 26 cout << "bool:" << "he" << c << "llo" << endl; 27 cout << "char:" << c << endl; 28 cout << "wchar_t：" << "he" << wc << "llo" << endl; 29 cout << "print array:" << endl; 30 for (int i = 0; i < 10; i ++) 31 { 32 cout << nArr[i] << " "; 33 } 34 cout << endl; 35 } 36private: 37 short sn; 38 int in; 39 long ln; 40 long long lln; 41 float f; 42 double d; 43 long double ld; 44 bool b; 45 char c; 46 wchar_t wc; 47 int nArr[10]; 48 49};
结果：
short:0
int:0
long:0
long long:0
float:0
double:0
long double:0
bool:he llo
char:
wchar_t：he32llo
print array:
0 0 0 0 0 0 0 0 0 0