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、...
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:
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...
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 thatmutableparameter...
Accessin the data "referred to" by a reference is the same as if the parameter were passed by value. Examples, to illustrate: int by_value( int x ) { return x + 5; } int by_pointer( const int* x ) { return x == NULL ? 0 : *x + 5; } // Returns 0 if x == NULL ...
This includes pass by value and pass by const reference, and excludes pass by non-const reference and pass by address. Returning structs Consider the case where we have a function that needs to return a point in 3-dimensional Cartesian space. Such a point has 3 attributes: an x-coordinate...
class C { public: void receive(const A& a) { B b; b.receive(a); } }; int main(int argc, char ** argv) { A a; C c; c.receive(a); return 0; } Solution: Assayhi()is declared asconst, it is necessary to declare all the functions it calls, includinghello()andworld(), ...
BOOL PtInRect(const RECT *lprc, POINT pt); Notice that you must pass the Rect structure by reference, since the function expects a pointer to a RECT type.VB 複製 Imports System.Runtime.InteropServices <StructLayout(LayoutKind.Sequential)> Public Structure Point Public x As Integer Public y ...
c. To cause to move as part of a process: pass liquid through a filter. d. To cause to go by: The sergeant passed his troops before the grandstand. e. To allow to cross a barrier: The border guard passed the tourists. f. Baseball To walk (a batter). g. To maneuver (the bull...
Because you use a C cast which removes the 'const' qualifier. Don't do that, it's a BAD IDEA(tm). [color=blue] > it_st->dumpState(); // <-- It cannot work. Why?[/color]The operator-> of 'const_iterator ' returns a reference to const 'state'. 'dumpState' is ...