Using regex for input validation - c++

Question

I know the following isn't the most efficient implementation (I could, after all, run regex_match() right in main() ) but it should still work, at least from my limited understanding.
I'm trying to use in C++11 to validate some input for dicerolls. I used expresso to build the regular expressions, and it validates it within expresso just fine. Why would it fail within this code?
#include <iostream>
#include <string>
#include <regex>
bool regexValidate (string expr, string teststring)
{
regex ex(expr);
if (regex_match(teststring,ex)) {
return true;
cout << "true";
} else if (regex_match (teststring,regex("^\s*\d*d\d*\s*$"))) {
return true;
cout << "true";
}
return false;
}
int main()
{
char choice; // menu option selected by user
bool isExit = false; // Is the user ready to exit?
// test code
string diceexpr = "^\s*\d{1,}d\d{1,}\s*$";
string teststr = "10d10";
string teststr1 = "1d10";
string teststr2 = " 10d10 ";
cout << teststr << " is ";
if (regexValidate(diceexpr,teststr)) {
cout << " valid!" << endl;
} else {
cout << " invalid!" << endl;
}
cout << teststr1 << " is ";
if (regexValidate(diceexpr,teststr1)) {
cout << " valid!" << endl;
} else {
cout << " invalid!" << endl;
}
cout << teststr2 << " is ";
if (regexValidate(diceexpr,teststr2)) {
cout << " valid!" << endl;
} else {
cout << " invalid!" << endl;
}
return 0;
}
Sample output:
10d10 is invalid!
1d10 is invalid!
10d10 is invalid!
RUN SUCCESSFUL (total time: 291ms)
UPDATE
Corrected my code and changed it to use the boost library for regular expressions.
#include <iostream>
#include <string>
#include <boost/regex.hpp>
using namespace std;
bool regexValidate (string expr, string teststring)
{
boost::regex ex(expr);
if ( boost::regex_match (teststring,ex) ) {
cout << "true";
return true;
//} else if (regex_match (teststring,regex("^\s*\d*d\d*\s*$"))) {
// cout << "true";
// return true;
}
return false;
}
int main()
{
string diceexpr = "^\\s*\\d{1,}d\\d{1,}\\s*$";
string teststr = "10d10";
string teststr1 = "1d10";
string teststr2 = " 10d10 ";
cout << teststr << " is ";
if (regexValidate(diceexpr,teststr)) {
cout << " valid!" << endl;
} else {
cout << " invalid!" << endl;
}
cout << teststr1 << " is ";
if (regexValidate(diceexpr,teststr1)) {
cout << " valid!" << endl;
} else {
cout << " invalid!" << endl;
}
cout << teststr2 << " is ";
if (regexValidate(diceexpr,teststr2)) {
cout << " valid!" << endl;
} else {
cout << " invalid!" << endl;
}
return 0;
}
Given the following output:
terminate called after throwing an instance of 'std::regex_error'
what(): regex_error
RUN FAILED (exit value 1, total time: 1s)

Answer 1

string diceexpr = "^\s*\d{1,}d\d{1,}\s*$";
This doesn't do what you think it does. In a string literal, "\s" is the same as "s" (you should be seeing compiler warnings about unrecognized escape sequences), while "\\s" represents two characters, backslash and 's'.
Double up all backslashes, or else use a raw string literal for your regular expression, as in
string diceexpr = R"(^\s*\d{1,}d\d{1,}\s*$)";