parsing - Requiring valid float input from stdin to have precision of 2 in C++ -

let reading float std::cin or file, , want enforce condition has 2 trailing decimal places:

e.g.
4.01 (valid)
4.001 (invalid - has 3 trailing decimal places)
a,47 (invalid, has 2 non [0-9] characters in 'a' , ',')
#556.53 (invalid, has '#')

(just context, in example, parsing text file several entries separated spaces, validating each input, , storing them in struct further processing.)

how it?

i found other sources in stackoverflow.

c++ how check input float variable valid input

here implementation. read string , accept if of characters not digits (in perl, suppose regex non-match [0-9]).

apparently, find_first_not_of method in string us:

  std::string a;    if(!(std::cin>>a)){     std::cout << "invalid float entry " << std::endl;   }    if(a.find_first_not_of("1234567890.-")!=std::string::npos){     std::cout << "invalid string float" << std::endl;} 

next, verify string has 2 decimal places searching location of decimal point.

  if(a.size()-a.find(".")!=3){     std::cout << "valid float must have 2 decimal places \n";   }else{     std::cout << "accept - valid float , has 2 decimal places \n";   } 

finally, convert float using stof.

float u = stof(a);