Would anyone do this differently?

i want to convert a string into a numerical value but there can be different data types...NumberType is <int || float || long || long double>

Code:

---

template<class NumberType> NumberType parse(const char &stringOfNumbers)
{
      //some parsing algorithm

    //isn't there a header with these defintions?
    NumberType convertedNumber;
    int  sizeFloat = sizeof(float);
    int longSize = sizeof(long);
    int longdoubleSize = sizeof(long double);

    switch(sizeof(NumberType))
    {
        case floatSize:
                    convertedNumber = atof(stringOfNumber, 10);              //stringOfNumbers = "1234.54"
                    break;
        case longSize:
                    convertedNumber = atol(stringOfNumbers, 10);
                    break;
          //.....................
    }

       

}

---

That's not quite right. You are passing in a const reference to a single character. Also, you cannot count on floats, longs, doubles, etc, being different sizes.

This type of function is quite easy using a stringstream. Any type that has an operator>> defined will work.

See http://www.parashift.com/c++-faq-lit....html#faq-38.1, 38.2, and 38.3 for examples of how to do this.

First create specialized functions, then call the funtion you want.

Code:

---

template<class type> type convert(type,type){
//..... general case
}
//specializations
template<float> float convert(const char* s){
    return atof(s,10);
}
template<double> double convert(const char* s){/**/}
template<short> short convert(const char* s){/**/}
template<long> long convert(const char* s){
    return atoi(s,10);
}
template<long long int> long long int convert(const char* s){/**/}
/*Then...*/
template<class NumberType> NumberType parse(const char &stringOfNumbers)
{
    //call specialized funtion...
    NumberType convertedNumber = convert<NumberType>(stringOfNumber);
/*..............................*/       
}

---

ok...thanks guys...i'll look into it (string stream & parashift)

i guess erath's version would work too...i wonder why i didn't think of that (rather it's the best way or not, i ussually would think of something like that)...


...but how would different (numerical) data types be the same size?...i'm just curious, not trying to argue.

this is a example to convert string into number:

Code:

---

#include<iostream>
#include<string>
#include<sstream>
using namespace std;

class calculation
{
private:

long double num1,num2;
char theoperator;
void calculate()
{
switch(theoperator)
{
case '+':
addition();
break;
case '-':
substraction();
break;
case '*':
multiplication();
break;
case '/':
if(!num2)
{cout<<"\ndenominator shouldn't be zero"<<endl;return;}
division();
break;
}
cout<<"="<<num1<<endl;
}
void addition()
{
num1+=num2;
}
void substraction()
{
num1-=num2;
}
void multiplication()
{
num1*=num2;
}
void division()
{
num1/=num2;
}

public:

void check(string input)
{
string num;
if(input.find("+",0)<input.size())
{
theoperator='+';
num=input.substr(0,input.find("+",0));
istringstream istream1(num);
istream1>>num1;
num=input.substr(input.find("+",0)+1,input.size()-input.find("+",0)-1);
istringstream istream2(num);
istream2>>num2;
}
else if(input.find("-",0)<input.size())
{
theoperator='-';
num=input.substr(0,input.find("-",0));
istringstream istream1(num);
istream1>>num1;
num=input.substr(input.find("-",0)+1,input.size()-input.find("-",0)-1);
istringstream istream2(num);
istream2>>num2;
}
else if(input.find("*",0)<input.size())
{
theoperator='*';
num=input.substr(0,input.find("*",0));
istringstream istream1(num);
istream1>>num1;
num=input.substr(input.find("*",0)+1,input.size()-input.find("*",0)-1);
istringstream istream2(num);
istream2>>num2;
}
else if(input.find("/",0)<input.size())
{
theoperator='/';
num=input.substr(0,input.find("/",0));
istringstream istream1(num);
istream1>>num1;
num=input.substr(input.find("/",0)+1,input.size()-input.find("/",0)-1);
istringstream istream2(num);
istream2>>num2;
}
else {cout<<"no operator"<<endl;return;}
calculate();
}

};

main()
{
string input;
calculation hoho;
while(1)
{
cin>>input;
hoho.check(input);
}
}

---

how abt something like this

Code:

---

#include <iostream>
#include <sstream>


using namespace std;


template<class NumberType>
NumberType parse(string a,NumberType b)
{
 

    NumberType convertedNumber;
    stringstream ss(a);
    ss >> b;
    return b;       
}   



int main( )
{
    double num;
    num=parse("1996.25",num);
    cout <<"\n"<< num;
   
   
    int num1;
    num1=parse("1996.25",num1);
    cout <<"\n"<< num1;
   
   
    getchar();
    return 0;
}

---

the 2nd parameter in the parse function is to tell that function what type of data to return...

that seems a bit too easy

It's not. And that's the beauty of templates.