Finding an alphanumeric character in a string using find_if and isalnum

Question

I'm using g++ 4.7.

What I'm trying to do is this,

find_if(s.begin(), s.end(), isalnum);

where isalnum is defined in cctype and s is a string.

logman.cpp:68:47: error: no matching function for call to ‘find_if(std::basic_string<char>::const_iterator, std::basic_string<char>::const_iterator, <unresolved overloaded function type>)’

However, this works,

bool my_isalnum(int c) {
    return isalnum(c);
}

find_if(s.begin(), s.end(), my_isalnum);

How can I get this to work without creating my own function?

If C++11 is ok for you, you could use a lambda expression. – jogojapan Nov 07 '12 at 02:46 — jogojapan, Nov 07 '12 at 02:46

score 8 · Accepted Answer · answered Nov 07 '12 at 03:02

8

The compiler is having trouble disambiguating between this function and this function. You want the first one, and you'll have to help the compiler out here, by specifying the signature with a cast:

find_if(s.begin(), s.end(), (int(*)(int))isalnum);

answered Nov 07 '12 at 03:02

Benjamin Lindley

101,917
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6

Note that adding the scope resolution operator `::isalnum` also works. – Jesse Good Nov 07 '12 at 03:15

score 2 · Answer 2 · answered May 08 '17 at 15:52

2

This should work.

#include <algorithm>
#include <cctype>
auto result = std::find_if (begin(s), end(s), std::isalnum);

answered May 08 '17 at 15:52

Calthron

21
1

score 0 · Answer 3 · edited Jun 01 '19 at 20:18

0

This should work

#include <algorithm >
#include <cctype>

auto result = std::find_if(std::begin(s), std::end(s),  isalnum) ;

edited Jun 01 '19 at 20:18

vimuth

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answered Jun 01 '19 at 19:51

Owl66

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12

Finding an alphanumeric character in a string using find_if and isalnum

3 Answers3

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