For example, pass vector reference // caller.cc std::vector<string> chip_ids; fn(chip_ids) //callee.cc void fn(const std::vector<string>& chip_ids) {do sth} Cases that use const reference: "All parameters passed by reference must be labeled const." This rule means that mutable par...
或者 int Test::func()const { string value = amap[0]; //amap是Test类的成员函数. } 用g++编译上面的代码,会报……discards qualifiers。 这里是原因。 简单来说,map的[]运算符会在索引项不存在的时候自动创建一个对象,有可能会改变map本身,所以不能够用在一个const map上。 解决办法有两个: 方法1、...
int Test::func()const { string value = amap[0]; //amap是Test类的成员函数.是就会产生传说中的null引用。 } 用g++编译上面的代码,会报……discards qualifiers。 这里是原因。 简单来说,map的[]运算符会在索引项不存在的时候自动创建一个对象,有可能会改变map本身,所以不能够用在一个const map上。 解决...
C++编程常见问题—error: passing 'const std::map<>]' discards qualifiers或pass-by-reference-to-const-map导致的“d } 解决办法有两个:
// Demonstrating functions with parameters of reference type.#include<iostream>#include<string>usingnamespacestd;boolgetClient( string& name,long& nr);voidputClient(conststring& name,constlong& nr);intmain()/*fromwww.java2s.com*/{ string clientName;longclientNr; ...
The solution is to pass things around by const reference (or const pointer in C). The cost of passing things around by const reference is trivial and about as expensive as passing around an int value. Not only is it so much more efficient to pass objects in this way, but the semantics...
对于像int这样的内置类型,写void f( const int& i )是没有意义的。传递变量的引用与传递值一样昂贵。 - xtofl 0 我会说 void cfunction_name(const X& a); 允许我将对临时对象的引用传递如下 X make_X(); function_name(make_X()); 当 void function_name(X& a); 未能实现此目标,出现...
const(// StatePending - initial state of a taskStatePending ="PENDING"// StateReceived - when task is received by a workerStateReceived ="RECEIVED"// StateStarted - when the worker starts processing the taskStateStarted ="STARTED"// StateRetry - when failed task has been scheduled for retry...
Example of Pass by Reference Consider the example: #include <iostream>usingnamespacestd;voidfun(int&b) { b=20; }intmain() {inta=10; fun(a); cout<<"Value of A: "<<a<<endl;return0; } Output Value of A: 20 Consider the function definition (or declaration)void fun(int &b), whil...
class testing{ int test1()const; // ... } int testing::test()const{ // ... } Reference:http://stackoverflow.com/questions/550428/an-odd-c-error-test-cpp15-error-passing-const-as-this-argument-of