is_int, C++ (vc++)

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//Microsoft (R) C/C++ Optimizing Compiler Version 19.00.23506 for x64

#include <iostream>
#include <regex>
#include <string>
#include <limits>
#include <cctype>
#include <iomanip>

bool is_int( const std::string& str ) { // check with regex (does not accept leading zeroes before first digit)

static constexpr auto max_digits = std::numeric_limits<int>::digits10 ;
    static const std::string ub = std::to_string(max_digits-1) ;
    static const std::regex int_re( "^\\s*([+-]?[1-9]\\d{0," + ub + "}|0)\\s*$" ) ;

return std::regex_match( str, int_re ) ;
}

bool is_int2( std::string str ) { // check with std::stoi (accepts any amount of leading zeroes)

try {

std::size_t pos = 0 ;
        std::stoi( str, std::addressof(pos) ) ;
        while( std::isspace( str.back() ) ) str.pop_back() ;
        return pos == str.size() ; // fully parsed except for white space at the end
    }

catch( const std::exception& ) { return false ; }
}

int main() {

std::cout << std::boolalpha ;

for( std::string str : { "  1234567  ", "+123", "1.23", "0", "-23", "2+3", "+-23", "123456789987654", "123 456", "00123" } )
        std::cout << std::quoted(str) << " : " << is_int(str) << ' ' << is_int2(str) << '\n' ;
}

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Compilation time: 2,54 sec, absolute running time: 0,21 sec, absolute service time: 2,76 sec