How do I fix "no match for call to" in recursion inside a function? (in a permutation recursion algorithm)

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void perm(std::string fixed,std::string perm){
    if (perm.length() == 1){
        std::cout << fixed + perm << std::endl;
    }else{
        for (int i=0;i<perm.length();i++){
            std::string perm2 = perm;
            std::swap(perm2[0],perm2[i]);
            perm(fixed + perm[i],perm2.substr(1,perm.length()-1));
        }
    }
}

This is my first question and I am (very) new to programming. I was working on a mini program which simply prints all the permutations of a string. For example, perm("","123") would be supposed to return the following values

123
132
213
231
312
321

However, on compilation, the g++ compiler returns the following error:

permutations.cpp: In function ‘void perm(std::string, std::string)’:
permutations.cpp:19:29: error: no match for call to ‘(std::string {aka 
std::__cxx11::basic_string<char>}) (std::__cxx11::basic_string<char>, 
std::__cxx11::basic_string<char>)’
19 |                         perm(fixed + perm[i],perm2.substr(1,perm.length()-1)); 
   |                         ~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

I would like to know the cause of this error and troubleshoot it. Thank you.

c++
2 Answers
void perm(std::string fixed,std::string perm){

You have a function called perm, and one of its parameters is also called perm, same name. Danger ahead.

perm(fixed + perm[i],perm2.substr(1,perm.length()-1));

According to rules of C++, the first perm here is a std::string object, one of the parameters to this function. This is not getting parsed as a recursive call to the same function, but an attempt to invoke a suitable operator() on a std::string object. Your C++ compiler is grumpy because no suitable overload was found.

Solution: don't use the same name for a function and one of its parameters.

user_39433120

The quick fix would be to specify that you want the function perm, not the std::string instance with the same name.

    ::perm(fixed + perm[i], perm2.substr(1, perm.length() - 1));
//  ^^

But I suggest that you change the name of one of them.

user_75822470
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