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; }
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. }
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]; };
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]; };
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