Is /proc/pid/maps a snapshot?

I wrote a little C++20 program that scans the address ranges of the process and logs its ranges, then makes an mmap() for 64kiB of memory and then looks if the ranges on the same opened file are still the same. They're not ! So /proc/pid/maps isn't a repeatable snapshot.

#include <iostream>
#include <regex>
#include <fstream>
#include <charconv>
#include <sstream>
#include <array>
#include <unistd.h>
#include <sys/mman.h>

using namespace std;

int main( int argc, char **argv )
{
    int pid = getpid();
    ostringstream oss;
    oss << "/proc/" << pid << "/maps";
    ifstream ifs( oss.str() );
    using range_t = pair<size_t, size_t>;
    static regex rxAddrsAndRd( "^([0-9a-f]{1,16})-([0-9a-f]{1,16}) *[rR]", regex_constants::ECMAScript | regex_constants::icase );
    match_results<string::iterator> mr;
    auto parse = [&]( auto fn )
        requires requires() { fn( range_t() ); }
    {
        ifs.clear();
        ifs.seekg( 0 );
        for( string line; getline( ifs, line ); )
        {
            if( !regex_search( line.begin(), line.end(), mr, rxAddrsAndRd ) )
                continue;
            array<size_t, 2> addrs;
            for( size_t a = 0; a <= 1; ++a )
                from_chars( to_address( mr[a + 1].first ), to_address( mr[a + 1].second ), addrs[a] );
            if( !fn( range_t( addrs[0], addrs[1] ) ) )
                return;
        }
    };
    vector<range_t> ranges;
    parse( [&]( range_t range ) { ranges.emplace_back( range ); return true; } );
    if( !mmap( nullptr, 0x10000, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS | MAP_POPULATE, -1, 0 ) )
        return EXIT_FAILURE;
    auto cmp = ranges.begin();
    bool equal = true;
    parse( [&]( range_t range )
        {
            if( cmp != ranges.end() && range == *cmp++ )
                return true;
            equal = false;
            return false;
        } );
    cout << (equal ? "snapshot" : "non-snapshot") << endl;
}