C++: Convert std::string to UINT64

Question

I need to convert a (decimal, if it matters) string representation of a number input from a text file to a UINT64 to pass to my data object.

    size_t startpos = num.find_first_not_of(" ");
    size_t endpos = num.find_last_not_of(" ");
    num = num.substr(startpos, endpos-startpos+1);
    UINT64 input;
    //convert num to input required here

Is there any way to convert an std::string to a UINT64 in a similar way to atoi()?

Thanks!

Edit: Working code below.

size_t startpos = num.find_first_not_of(" ");
size_t endpos = num.find_last_not_of(" ");
num = num.substr(startpos, endpos-startpos+1);
UINT64 input; //= std::strtoull(num.cstr(), NULL, 0);

std::istringstream stream (num);
stream >> input;

It's for a project I'm working on using existing structures. That's just the structure of the object in my case. — George G, Jul 19 '16 at 12:42

score 4 · Answer 1 · 2016-07-19T12:52:17.470

4

Use strtoull or _strtoui64(). Example:

std::string s = "1123.45";
__int64 n = std::strtoull(s.c_str(),NULL,0);

edited Jul 19 '16 at 12:52

answered Jul 19 '16 at 10:47

Thanks! I'm trying to search how I can get the pointers to the beginning and end of the std::string, but havn't found anything yet. Do you know how I can get these? – George G Jul 19 '16 at 12:44
@IpqD I have updated the answer. Regarding the string, there are: [string.begin()](http://www.cplusplus.com/reference/string/string/begin/) and [string.end()](http://www.cplusplus.com/reference/string/string/end/) iterators. – Jul 19 '16 at 12:53
Thanks again :). I included the library, but my project seems to say that std has no member "strtoull". Would you know if this is something I have done wrong? Also, is there a difference between __int64 and UINT64? – George G Jul 19 '16 at 13:02
1

`uint64_t` is the standard fixed length 64 bit unsigned integer type. It is an optional part of the C standard, defined in ``, in C++ therefore in ``. – Jan Henke Jul 19 '16 at 13:17

score 2 · Accepted Answer · edited Jul 19 '16 at 12:55

2

There are at least two ways to do this:

Construct a std::istringstream, and use our old friend, the >> operator.
Just convert it yourself. Parse all the digits, one at a time, converting them to a single integer. This is a very good exercise. And since this is an unsigned value, there isn't even a negative number to worry about. I would think that this would be a standard homework assignment in any introductory computer science class. At least it was, back in my days.

edited Jul 19 '16 at 12:55

Cody Gray - on strike

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answered Jul 19 '16 at 10:50

Sam Varshavchik

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The istringstream method worked for me. Thank you :) – George G Jul 19 '16 at 13:03

dima.rus · Answer 3 · 2019-02-26T09:20:08.103

0

you can use stoull:

char s[25] = "12345678901234567890"; // or: string s = "12345678901234567890";
uint64_t a = stoull(s);

edited Feb 26 '19 at 09:20

answered Feb 25 '19 at 11:52

dima.rus

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C++: Convert std::string to UINT64

3 Answers3