[英]no known conversion for templated vs const non-templated vector
In my actual code, I included a library, and as soon as I did that, it started crashing. 在我的实际代码中,我包含了一个库,一旦这样做,它便开始崩溃。 I managed to sort of extract some of that code into this minimal example, that demonstrates the same kind of error:
我设法将一些代码提取到这个最小的示例中,该示例演示了相同类型的错误:
// g++ -std=c++11 -g -o test-classcall.exe test-classcall.cpp
#include <iostream>
#include <vector>
#include <stdio.h>
class Cat
{
public:
int Age;
Cat() : Age(0) {}
};
std::vector<Cat> myPCats;
typedef std::vector<Cat> TDVectCats;
TDVectCats myTDCats;
void loopSomeCats() {
printf("this function just to cause searching for matching calls\n");
}
void loopSomeCats(TDVectCats& incats) {
std::vector<Cat>::iterator iter;
for(iter = incats.begin(); iter != incats.end(); iter++) {
printf("hm\n");
}
}
const std::vector<Cat> & getSomeCats() {
return myPCats;
}
void doSomething() {
loopSomeCats(getSomeCats());
}
int main() {
myTDCats.push_back(Cat());
myTDCats.push_back(Cat());
myPCats.push_back(Cat());
doSomething();
std::cout << "Hello World! " << std::endl;
return 0;
}
The result is: 结果是:
$ g++ -std=c++11 -g -o test-classcall.exe test-classcall.cpp
test-classcall.cpp: In function ‘void doSomething()’:
test-classcall.cpp:36:29: error: no matching function for call to ‘loopSomeCats(const std::vector<Cat>&)’
loopSomeCats(getSomeCats());
^
test-classcall.cpp:36:29: note: candidates are:
test-classcall.cpp:20:6: note: void loopSomeCats()
void loopSomeCats() {
^
test-classcall.cpp:20:6: note: candidate expects 0 arguments, 1 provided
test-classcall.cpp:24:6: note: void loopSomeCats(TDVectCats&)
void loopSomeCats(TDVectCats& incats) {
^
test-classcall.cpp:24:6: note: no known conversion for argument 1 from ‘const std::vector<Cat>’ to ‘TDVectCats& {aka std::vector<Cat>&}’
What especially confuses me, is the last "no known conversion for argument 1 from 'const std::vector<Cat>' to 'TDVectCats& {aka std::vector<Cat>&}'", as if it cannot convert a vector of something, into the vector of the same something, just because of typedef
? 令我特别困惑的是最后一次“未知的将参数1从'const std :: vector <Cat>'转换为'TDVectCats&{aka std :: vector <Cat>&}''”,就好像它无法转换向量一样只是因为
typedef
导致某物进入同一物的向量? Or it maybe has to do with the const
- but I simply cannot see what I need to change, in order to have a call like loopSomeCats(getSomeCats());
或者它可能与
const
-但我根本看不到需要更改什么,才能进行loopSomeCats(getSomeCats());
类的调用loopSomeCats(getSomeCats());
succeed... 成功...
You can't pass a reference to a const
object to a non-const reference. 您不能
const
对象的引用传递给非const引用。
loopSomeCats
takes a std::vector<Cat>&
as argument, and you want to pass a const std::vector<Cat>&
to it, but that's not possible. loopSomeCats
将std::vector<Cat>&
作为参数,并且您想向其传递const std::vector<Cat>&
,但这是不可能的。
The const
would mean that you don't want anyone to modify the return value, but if you pass it to a function which just takes a non-const reference, then theoretically the function can modify the reference, and you don't want that. const
表示您不希望任何人修改返回值,但是如果将其传递给仅接受非const引用的函数,则理论上该函数可以修改该引用,而您不希望这样做。
You should drop the const
if you want the return value to be modified. 如果要修改返回值,则应删除
const
。
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