类成员变量的初始化
<p>C++11中在初始化时可以使用 = ，也可以使用 {} ，也可以使用 ={} ；</p><p>需要注意的是：类中的静态成员变量只有<strong>静态常量，并且类型是整型或者枚举类型，才能在类内初始化，其他都得在类外初始化。</strong></p>
<pre><code class="language-c++">#include <iostream>
using namespace std;
class Base {
public:
Base(){
}
Base(int num){
}
int a = { 4 };
int b{ 1 };
double cc = 1.23;
char aa = 'a';
string str = "hello";
string str1{ "world" };
//string str2("hello,world"); //用（）则会报错，类内不能用()初始化，在类外这个是有参构造，可以使用。
string str3 = { "hello" };
static int c;
static const double d;
static const char* const e;//静态常量字符数组指向静态字符数组
// 变量是静态常量，并且类型是整型或者枚举类型，才能在类内初始化，其他都得在类外初始化。
const static int f = 0;//const static 和 static const 意义相同，没有区别
};
int Base::c = 8;
const double Base::d = 3.14;
const char* const Base::e = "i am luffy";
int main() {
int ab { 4 };
string str7 = { "hello" };
string str8("888");
string str9 { "888888" };
return 0;
}
</code></pre>
<p>另外还提供了初始化列表：</p>
<pre><code class="language-c++">#include <iostream>
using namespace std;
class c {
public:
c() :m_num(66), a(3), b(3) {
}
c(int n1, int n2, int n3) : m_num(n1),a(n2), b(n3){
}
int m_num = 8;
int a;
int b;
};
int main() {
c c1;
c c2(11,22,33);
cout << "c1.m_num = " << c1.m_num << "c1.a = " << c1.a << "c1.b = " << c1.b << endl;
cout << "c2.m_num = " << c2.m_num << "c2.a = " << c2.a << "c2.b = " << c2.b << endl;
system("pause");
return 0;
}
</code></pre>
<p>输出结果：</p>
<pre><code class="language-c++">c1.m_num = 66c1.a = 3c1.b = 3
c2.m_num = 11c2.a = 22c2.b = 33
</code></pre>
<p>使用初始化列表初始化成员变量</p>
<p>且从上面的程序中说明先运行了<code>int m_num = 8;</code>之后才进行初始化的<code>m_num{66}</code>;</p>
<p>那么和之前的<code>this->m_num = a;</code>初始化方式比较谁先运行呢？</p>
<pre><code class="language-c++">class c {
public:
c(int n1, int n2, int n3) : m_num(n1),a(n2), b(n3){
this->m_num = 99999;
}
int m_num = 8;
int a;
int b;
};
int main() {
c c2(11,22,33);
cout << "c2.m_num = " << c2.m_num << "c2.a = " << c2.a << "c2.b = " << c2.b << endl;
system("pause");
return 0;
}
</code></pre>
<p>输出结果：</p>
<pre><code class="language-c++">c2.m_num = 99999c2.a = 22c2.b = 33
</code></pre>
<p>说明<code>this->m_num = 99999;</code>这种初始化方式是最后执行的。</p><br><br>
来源：https://www.cnblogs.com/ggkx/p/19342325
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