Why does g++ mark a casting error at not executed code?

Question

main:

#include "multiparse.h"

int main()

{
    parse_string obj;
    obj = "1234";
    //int a = obj;
    //obj = 1234;
    return 0;
}

header:

class parse_string
{
char* str;
long str_sz;
double val;
bool isnumber;
public:
template<class typename>
    parse_string& operator=(typenamet input)
    {
        //printf("%d == %d\n",typeid(input).name(),typeid(const char*).name());
        if(typeid(input)==typeid(char*)||typeid(input)==typeid(const char*))
        {
            str_sz=strlen(input)+1;
            if(str==0)
            {
                str = (char*)malloc(sizeof(char)*str_sz);
            }
            else
            {
                str = (char*)realloc(str,sizeof(char)*str_sz);
            }
            memset(str,0,str_sz);
            strcpy(str,input);
            this->str_to_num();
            isnumber=0;
            printf("A\n");
        }
        else
        {
            printf("B\n");
            val = (double)input;
            this->num_to_str();
            isnumber=1;
        }
    }
};

g++ error: multiparse.h error: invalid cast from type 'const char*' to type 'double' at --> 'val = (double)input;'

This code is not executed in my case it will just printf 'A' and not 'B', but g++ doesn't compile this code. I can't figure it out.

Answer 1

I found a solution for my requirements, but I think it's not the best way:

parse_string& operator=(char* input)
    {
            str_sz=strlen(input)+1;
            if(str==0)
            {
                str = (char*)malloc(sizeof(char)*str_sz);
            }
            else
            {
                str = (char*)realloc(str,sizeof(char)*str_sz);
            }
            memset(str,0,str_sz);
            strcpy(str,input);
            this->str_to_num();
            isnumber=0;
            return *this;
    }

    parse_string& operator=(const char* input)
    {
            str_sz=strlen(input)+1;
            if(str==0)
            {
                str = (char*)malloc(sizeof(char)*str_sz);
            }
            else
            {
                str = (char*)realloc(str,sizeof(char)*str_sz);
            }
            memset(str,0,str_sz);
            strcpy(str,input);
            this->str_to_num();
            isnumber=0;
            return *this;
    }

    parse_string& operator=(char input)
    {
            val = (double)input;
            this->num_to_str();
            isnumber=1;
            return *this;
    }
    parse_string& operator=(int input)
    {
            val = (double)input;
            this->num_to_str();
            isnumber=1;
            return *this;
    }
    parse_string& operator=(long input)
    {
            val = (double)input;
            this->num_to_str();
            isnumber=1;
            return *this;
    }
    parse_string& operator=(unsigned char input)
    {
            val = (double)input;
            this->num_to_str();
            isnumber=1;
            return *this;
    }
    parse_string& operator=(unsigned int input)
    {
            val = (double)input;
            this->num_to_str();
            isnumber=1;
            return *this;
    }
    parse_string& operator=(unsigned long input)
    {
            val = (double)input;
            this->num_to_str();
            isnumber=1;
            return *this;
    }
    parse_string& operator=(double input)
    {
            val = input;
            this->num_to_str();
            isnumber=1;
            return *this;
    }

Answer 2

Even though, the code is not executed, it's still part of a *.cpp file (as it was #included. So, it becomes apart of a *.obj/*.o file for this source. For this to happen, compiler needs to generate machine code for everything in the *.cpp file (templates work a bit different, but it's not about them now).

In other words, to get a .exe/.lib/.dll file, which consists of .obj files, you need the the files which are to become said .obj files to be compiled properly (transcoded to machine code).