string::substr(begin, end)

[Justin_]

Hi friends.

There is something screwy going on with the substr method. Here's my code.

c++:

int Hex::ConvertToInt(std::string hexNum) {     int num = 66;  //66 is an arbitrary initial value.     std::cout << hexNum << std::endl;     //transform(hexNum.begin(), hexNum.end(),hexNum.begin(), tolower);     for (int i = 0; i <= 15; i++)     {        std::cout << "i= " << i << std::endl;        std::cout << "substr= " << hexOrder.substr(i, i+1) << " ";        if (hexNum == hexOrder.substr(i, i+1))        {           num = i;           break;        }     }     std::cout << num;     return num; }

here is the output:

code:

a i= 0 substr= 0 i= 1 substr= 12 i= 2 substr= 234 i= 3 substr= 3456 i= 4 substr= 45678 i= 5 substr= 56789a i= 6 substr= 6789abc i= 7 substr= 789abcde i= 8 substr= 89abcdef i= 9 substr= 9abcdef i= 10 substr= abcdef i= 11 substr= bcdef i= 12 substr= cdef i= 13 substr= def i= 14 substr= ef i= 15 substr= f 66

the problem is that for each substring there should only be one character. For instance, if the substring was (0,1) only one character is printed. If i=0, then i + 1= 1 and thus (0,1). It should consistantly only be one character but you see, each time it goes it gets to be more characters all the way up to i=8 and then it retracts again. Why? And how to fix?

[wtd]

Try looking at the docs.

basic_string::substr takes two arguments. The first is the starting index, and the second is the count of characters.

You may wish to use the "at" member function instead, though.

[Justin_]

okay, thanks.

[wtd]

Oh, and you're working too hard.

code:

#include <iostream> #include <sstream> #include <string> int main() {     std::string hex_as_string = "FF";     std::stringstream ss(hex_as_string);     int num;     ss >> std::hex >> num;     std::cout << num << std::endl;     return 0; }

[Justin_]

Where there are comments I am unsure of what is taking place. Where there are not comments, I know what is taking place.

c++:

#include <iostream> #include <sstream> #include <string> int main() {     std::string hex_as_string = "FF";     std::stringstream ss(hex_as_string) //initializing ss to "FF";     int num;     ss >>//whats this? std::hex //whats this? >> num;     std::cout << num << std::endl;     return 0; }

[Andy]

read up on wtd's stringstream tutorial

found here

[wtd]

Streams work a little differently with some values than with others.

The std::hex variable, for instance, tells the stream that that next thing should be treated as a hexidecimal number.

[Justin_]

good stuff

[Justin_]

there doesn't seem to be an std::bin, how should I convert decimal to binary?

[wtd]

You're gonna have to do that one the hard way. But even then, it's not that hard. Before you start writing code, really think about how you'd do it by hand.