c++ - no matching function for call to

Question

My terminal messages

zo@laptop:~/Desktop$ g++ stack.cpp 
stack.cpp: In function ‘int main(int, char**)’:
stack.cpp:50:19: error: no matching function for call to ‘boyInitial(Boy [boyNumber])’
     boyInitial(boy);
                   ^
stack.cpp:17:6: note: candidate: template<class T, int N> void boyInitial(T (&)[N])
 void boyInitial(T (&boy)[N]){
      ^~~~~~~~~~
stack.cpp:17:6: note:   template argument deduction/substitution failed:
stack.cpp:50:19: note:   variable-sized array type ‘long int’ is not a valid template argument
     boyInitial(boy);
                   ^
stack.cpp:51:19: error: no matching function for call to ‘getBoyAges(Boy [boyNumber])’
     getBoyAges(boy);
                   ^
stack.cpp:34:6: note: candidate: template<class T, int N> void getBoyAges(T (&)[N])
 void getBoyAges(T (&boy)[N]){
      ^~~~~~~~~~
stack.cpp:34:6: note:   template argument deduction/substitution failed:
stack.cpp:51:19: note:   variable-sized array type ‘long int’ is not a valid template argument
     getBoyAges(boy);

My Program

#include <iostream>

class People{
    public:
        char *name;
        int age;
};

class Boy : public People{
    public:
        void say(void){
            std::cout << "i`m the most handsome!" << std::endl;
        }
};

template<class T, int N> 
void boyInitial(T (&boy)[N]){
    int i;
    for(i=0;i<N;i++){
        std::cout << "please input boy No." << i+1 << "`s age" << std::endl;
        std::cin >> boy[i].age; 
    }
}

template<class T, int N>
void getBoyAges(T (&boy)[N]){
    int i;
    for(i=0;i<N;i++){
        std::cout << boy.age << std::endl;
    }
}

int main(int argc, char **argv){
    using namespace std;
    int boyNumber = 0;
    cout << "how many boys do you want?" << endl;
    cin >> boyNumber;
    Boy boy[boyNumber];
    boyInitial(boy);
    getBoyAges(boy);
    return 0;
}

Description

I'm trying to deliver Boy-type data boy, to the functions boyInitial() and getBoyAges(), by means of references, and then I get such errors.

I am trying to imitate the code here, and then get the errors.

I`d appreciate your help!

`variable-sized array type ‘long int’ is not a valid template argument` says it all. — Retired Ninja, Jul 12 '21 at 11:19
This is the first time i\`ve asked on this website, i\`ll remember not to post code in images. Thank you all for the fast respond, which is out of my expect! — Zohar-fzh, Jul 12 '21 at 11:54
When I changed the image into text of code. It says "please add more details, your code is too much", so maybe I`d just leave the image here. Anyway, thanks! — Zohar-fzh, Jul 12 '21 at 11:57

Vlad from Moscow · Accepted Answer · 2021-07-12T12:01:13.097

The key error message is the following

note: variable-sized array type ‘long int’ is not a valid template argument

You declared a variable length array (the size of the array is not a constant expression)

int boyNumber = 0;
cout << "how many boys do you want?" << endl;
cin >> boyNumber;

Boy boy[boyNumber];

that is not a standard C++ feature.

Instead of variable length arrays use the standard container std::vector.

The presented last program works because there is no variable length array. The size of the array is known at the compile time.

At least you could declare the functions like for example

template<class T> 
void boyInitial(T *boy, size_t n ){
    for( size_t i=0; i < n; i++){
        std::cout << "please input boy No." << i+1 << "`s age" << std::endl;
        std::cin >> boy[i].age; 
    }
}

The function can be called like

boyInitial( boy, boyNumber );

fwiw, also `std::vector` will fail with `boyInitial`, but the fix for that is much simpler than to keep the templates the way they are — 463035818_is_not_an_ai, Jul 12 '21 at 11:22
After using std::vector and delete the template things, the code was built well. — Zohar-fzh, Jul 12 '21 at 12:12

c++ - no matching function for call to

My terminal messages

My Program

Description

1 Answers1