How to do a true strtoul? Wont intake an actual string

Question

Having an issue inputting an ACTUAL string to strtuol. The input string SHOULD be an unsigned binary value of 32 bits long.

Obviously, there is in issue with InputString = apple; but I'm not sure how to resolve the issue. any thoughts? This shouldnt be that difficult. not sure why I'm having such a hard time with it.

Thanks guys.

#include <iostream>
#include <string>
#include <sstream>
using namespace std;
int main()
{
    char InputString[40];
    char *pEnd = NULL;          // Required for strtol()
    string apple = "11111111110000000000101010101000";
    //cout << "Number? ";
    //cin >> InputString;
    InputString = apple;
    unsigned long x = strtoul(InputString, &pEnd, 2);     // String to long

    cout << hex << x << endl;
    return 1;
}

Can you use [`std::stoul`](http://en.cppreference.com/w/cpp/string/basic_string/stoul) instead? It takes a `std::string` directly. — Blastfurnace, Oct 03 '13 at 16:45
Um, the input string should be a sequence of 32 **characters**, each being `1` or `0`. The string does not have a numeric value. — Pete Becker, Oct 03 '13 at 16:55

Zac Howland · Answer 1 · 2013-10-03T17:12:11.883

1

A better approach would be to avoid the legacy-C functions and use the C++ standard functions:

string apple = "11111111110000000000101010101000";
unsigned long long x = std::stoull(apple, NULL, 2); // defined in <string>

NOTE: std::stoull will actually call ::strtoull internally, but it allows you to just deal with the std::string object instead of having to convert it to a C-style string.

edited Oct 03 '13 at 17:12

answered Oct 03 '13 at 17:01

Zac Howland

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I agree with this answer but `std::stoul` is a better match for the example code in the question. – Blastfurnace Oct 03 '13 at 17:24
@Blastfurnace If his string was 32 characters long, I would agree. Since it is 33 characters long (and his current C-style string is 40 characters), a 64-bit version of the function is a better match. They are in the same family of functions, however (and both are declared in ``. – Zac Howland Oct 03 '13 at 18:01

P0W · Accepted Answer · 2013-10-03T16:51:29.997

0

Include :

#include<cstdlib> // for strtol()
#include<cstring> // for strncpy()

and then

 strncpy(InputString ,apple.c_str(),40); 
                            ^
                            |
                            convert to C ctring

Or simply,

unsigned long x = strtoul(apple.c_str(), &pEnd, 2);

edited Oct 03 '13 at 16:51

answered Oct 03 '13 at 16:39

P0W

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Shouldn't you use strncpy to avoid buffer overflow? For that matter, why copy the string at all; why not use apple.c_str() directly in strtoul()? – Cookyt Oct 03 '13 at 16:45
Works perfect. and elimintaes the need to use `inputstring` thanks guys. – cmonnats23 Oct 03 '13 at 16:49
@cmonnats23 - while `strncpy` avoids overflowing the buffer, if the input string is the same size as the buffer `strncpy` does **not** append a terminating nul character and you have a garbage string. – Pete Becker Oct 03 '13 at 16:58

How to do a true strtoul? Wont intake an actual string

2 Answers2