Question

i have following code

#include <iostream>
#include <string>
using namespace std;
string generate(){
     for (char c1='A';c1<='Z';c1++){
          for (char c2='A';c2 <='Z';c2++){
               for (char c3='A';c3<='Z';c3++){
                    for (char c4='A';c4<='Z';c4++){


                         return  (new string *)(c1) + (new string*)(c2)+(new string*)(c3)+(new string*)(c4);
                    }
               }
          }
     }


}
int main(){




     return 0;
}

i want to generate strings but here is error

1>------ Build started: Project: string_combinations, Configuration: Debug Win32 ------
1>Build started 9/11/2010 12:42:08 PM.
1>InitializeBuildStatus:
1>  Touching "Debug\string_combinations.unsuccessfulbuild".
1>ClCompile:
1>  string_combinations.cpp
1>c:\users\david\documents\visual studio 2010\projects\string_combinations\string_combinations\string_combinations.cpp(11): error C2064: term does not evaluate to a function taking 1 arguments
1>c:\users\david\documents\visual studio 2010\projects\string_combinations\string_combinations\string_combinations.cpp(11): error C2064: term does not evaluate to a function taking 1 arguments
1>c:\users\david\documents\visual studio 2010\projects\string_combinations\string_combinations\string_combinations.cpp(11): error C2064: term does not evaluate to a function taking 1 arguments
1>c:\users\david\documents\visual studio 2010\projects\string_combinations\string_combinations\string_combinations.cpp(11): error C2064: term does not evaluate to a function taking 1 arguments
1>
1>Build FAILED.
1>
1>Time Elapsed 00:00:00.82
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

please help i am confused why i can’t directly convert from char to string by this method string(char)

Answer 1

The problem is with your expressions of this form:

(new string *)(c1)

The left hand side isn’t a type, it’s an expression. When you suffix it with another parenthesized expression it looks like a function call but that only works if the left expression is a function name or function pointer. In this case the new expression has type std::string** which isn’t a function pointer.

To construct a temporary string from a single char, you shouldn’t use new which dynamically allocates an object; instead you can use a constructor. A suitable one is the one which takes a count and a char to repeat for that count. In your case a count of 1 is what you want:

std::string(1, c1);

You can do something like.

return std::string(1, c1) + std::string(1, c2);

Note that you also don’t call generate anywhere and if you do return from the first iteration of a for loop you aren’t going to be iterating through all the combinations, you will only every generate the first compination.