Find the first character that is not whitespace in a std::string

问题

Lets say I have

std::wstring str(L"   abc");

The contents of the string could be arbitrary.

How can I find the first character that is not whitespace in that string, i.e. in this case the position of the 'a'?

回答1:

This should do it (C++03 compatible, in C++11 you can use a lambda):

#include <cwctype>
#include <functional>

typedef int(*Pred)(std::wint_t);
std::string::iterator it =
    std::find_if( str.begin(), str.end(), std::not1<Pred>(std::iswspace) );

It returns an iterator, subtract str.begin() from it if you want an index (or use std::distance).

回答2:

use [std::basic_string::find_first_not_of][1] function

std::wstring::size_type pos = str.find_first_not_of(' ');

pos is 3

Update: to find any other chars

const wstring delims(L" \t,.;");
std::wstring::size_type pos = str.find_first_not_of(delims);

来源：https://stackoverflow.com/questions/22658597/find-the-first-character-that-is-not-whitespace-in-a-stdstring