C++中内置变量的初始化

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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: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：

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 <iostream>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:-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

#pragma once#include <iostream>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: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

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