- int argc ，char * argv[] - argument count & argument vector
argc - 命令行参数个数，argv[]依次指向每一个命令行参数，其中argv[0]为程序名字：下面的程序包含了完整的程序路径。
#include <iostream> int main(int argc, char *argv[])
{ int i = ; // begin with 0
while (i < argc)
std::cout << argv[i++] // output string
<< " " // output SPACE
<< std::endl; // terminate output line
return ;
}
引用
1）作为返回值，不需要产生临时对象，然后拷贝这个对象，（见下面代码的注释），目前不要深究引用机制，目前记住的返回引用的场景：输入流、 //发现其他的再补充
// 2019-11-24日更新,对于引用作为返回值类型,可以通过汇编可知返回的是结果的地址值(引用视为弱化指针).在C++语法层面上考虑,就是首先,这个函数可以作为左值,是可以赋值的,如在重载[](下标索引)的时候,返回非应用是查值,返回引用,则可以进行赋值.其次,根据上面的说明,返回类型为引用的函数的一大作用就是给函数作用域外的值赋值.这个作用在我这个例子中几乎体现不出来,这是以前总结的时候忽略的,所以在此说明.
-
#include <iostream>
using namespace std; int & rfun(int &); //don't dig more,ref func saves time.
int fun(int); void main(void) {
int a = , b = ;
int &ra = a, &rb = b; //Treat ra as another name of a
int *pa = &ra, *pb = &rb; cout << pa << " " << (void *)pa << endl;
cout << pb << " " << (void *)pb << endl; cout << a << " " << b << endl;
cout << rb << " " << (void *)&rb << endl; //&rb == pb always.
rb = rfun(ra); //b=ra; rb=ra; --> int &rd=a;
//rb=fun(ra);
cout << rb << " " << (void *)&rb << endl; cout << a << " " << b << endl;
rb = ;
cout << a << " " << b << endl;
} int & rfun(int & r) {
return r; // b=fun(a) --> b=a;
}; int fun(int r) {
return r; // b=fun(a) --> r=a; b=r;
};2）引用类型参数
对于class，vector等类型的参数，引用 避免了值拷贝，提升效率，使用引用，函数可以改变实参的值，如果在调用过程中实参值不会发生变化，那么添加 const 修饰。
//call by ref can change the value after func called.
#include <iostream> using namespace std; void funr(const int &, int);
int& rfun(const int &, int); void main(void) {
int a = ;
int& b = a;
const int& c = ; const int & ca = a; a = ; const int cb = ; cout << &a << " " << a << endl;
cout << &b << " " << b << endl;
cout << &c << " " << c << endl; cout << endl << endl; funr(a, a); //first a,like above;second a, int tmp = a;
funr(, );
cout << endl << endl; int& rf = rfun(c, c);
cout << &rf << " " << rf << endl; } void funr(const int & ra, int pa) {
cout << &ra << " " << ra << endl;
cout << &pa << " " << pa << endl; //int tmp = pa, &pa is addr of tmp
} int& rfun(const int & ra, int pa) { // b = rfun(ra,pa)-->b = ra int x = , &d = x;
cout << &ra << " " << ra << endl;
cout << &pa << " " << pa << endl;
return (int&)ra;
}
以上则是目前想到的关于引用的知识点小结，以前曾经写过这话题的博文，今天讲解细致些，看注释，运行程序，更快速理解引用，VS2015社区版。
2016-5-21补充代码如下：
#include <iostream>
using namespace std; class A {
public:
int a;
A(int = );
A(const A &);
A& operator = (const A &); void PV(A);
void PR(A&);
A RV(void);
A& RR(void);
}; // A A::A(int x) : a(x) { cout << "Constructor (value)" << endl; }
A::A(const A & x) { cout << "Constructor (copy)-" << (void *)&x << endl; a = x.a; } A& A::operator = (const A & x) { cout << "Operator (=) @ " << (void *)&x << endl; a = x.a; return *this; } void A::PV(A x) { cout << "Calling By Value @ " << (void *)&x << endl; }
void A::PR(A &x) { cout << "Calling By Refe. @ " << (void *)&x << endl; } A A::RV(void) { cout << "Calling Rt Value" << endl; return *this; }
A& A::RR(void) { cout << "Calling Rt Refe." << endl; return *this; } int main(void) {
A oa, ob(); cout << "oa @ " << (void *)&oa << endl;
cout << "ob @ " << (void *)&ob << endl; cout << endl << "" << endl;
oa.PR(ob);
cout << endl << "" << endl;
oa.PV(ob);
cout << endl << "" << endl; ob = oa.RR();
cout << endl << "" << endl; ob = oa.RV();
cout << endl << "" << endl;
return ;
}
参数类型为class且为值传递的时，先调用对象的拷贝构造函数生成中间值，然后传入这个中间值到函数中；返回类型为值类型的时，会调用拷贝构造函数生成中间值，实际上返回的是这个中间值。