CERT C++: ERR62-CPP

The issue occurs when you perform string-to-number conversion using the formatted input stream std::basic_istream and the locale facet num_get<> but do not check for errors. For instance, Polyspace^® reports a violation when:

String-to-number conversions can produce errors such as:

Unexpected behavior can occur if you assume that string-to-number conversions result in a valid state without checking for errors.

To fix this violation, check the string-to-number conversion for errors when using :

This example code performs string-to-number conversion by using std::basic_istream::operator>> outside a try-catch block. An exception arising from the std::basic_istream::operator>> operator becomes an uncaught exception, causing the program to terminate prematurely. Because the code calls std::basic_istream::operator>> outside a try-catch block, Polyspace reports violations of this rule.

#include <iostream>
void stringConversionNotValidated(){
	int i,j;
	//...
	std::cin>>i;
	
	try{
		std::cin>>j;  //Noncompliant
	}catch (std::istream::failure &E) {
    // Handle error
  }
	
}//Noncompliant

Fix the violations by checking for exceptions when using std::basic_istream::operator>>. In this example code, calls to std::cin>> take place within a try-catch block. Because this code activates std::cin.exceptions, conversion exceptions are caught and handled in the catch block.

#include <iostream>
void stringConversionValidated() {
  int i, j;
 
  std::cin.exceptions(std::istream::failbit | std::istream::badbit);
  try {    
    std::cin >> i >> j;
    // ...
  } catch (std::istream::failure &E) {
    // Handle error
  }
}

Fix the violations by checking for conversion errors when using std::basic_istream::operator>>. In this example code, after calling std::cin>>, the function std::cin.fail() is called in an if block to check for and handle conversion errors.

#include <iostream>
void stringConversionNotValidated(){
	int i,j;
	//...
	std::cin>>i;
	 if (std::cin.fail()) {
    // Handle failure to convert the value.

  }
	try{
		std::cin>>j;  //Compliant
		if (std::cin.fail()) {
    // Handle failure to convert the value.

  }
	}catch (std::istream::failure &E) {
    // Handle error
  }
	
}//Compliant	

In this example, the function numGetNotTested() calls std::num_get<>::get() to convert strings to numbers, but does not check if the operation results in a valid state. Polyspace reports a violation.

#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <locale>
#include <iterator>

void numGetNotTested(std::string& str){
    std::istringstream s(str);
    s.imbue(std::locale()); // using default "C" locale
    auto& fac = std::use_facet<std::num_get<char>>(s.getloc());
    std::istreambuf_iterator<char> beg(s), end;
    double f;
    std::ios::iostate err = std::ios_base::goodbit;
    fac.get(beg, end, s, err, f); 
	
}//Noncompliant 

To fix this violation, check the call to std::num_get<>::get() for errors. For instance, in this code, after calling fac.get(), the error state of the call is tested in the if() block. Polyspace does not report a violation.

#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <locale>
#include <iterator>

void numGetTested(std::string& str){
    std::istringstream s(str);
    s.imbue(std::locale()); // using default "C" locale
    auto& fac = std::use_facet<std::num_get<char>>(s.getloc());
    std::istreambuf_iterator<char> beg(s), end;
    double f;
    std::ios::iostate err = std::ios_base::goodbit;
    fac.get(beg, end, s, err, f); 
	if (err == std::ios_base::badbit) {
        //...
    }
}