String validation for user input

Question

0.00/5 (No votes)

See more:

i am doin strin validation ,when ever user give input as below characters i ahve throw error like not valid string.
" / \ [ ] : ; | = , + * ? < >

but i am getting error as
"Microsoft C++ exception: std::regex_error at memory location 0x000000000019A210."

What I have tried:

bool ValidateLoginid(CString inputString)
{std::regex stringpattern("[!/\[]:;|=,+*<>]*");

std::string s_input(CW2A(inputString.GetString()));
if (std::regex_match(s_input, stringpattern))
{
return false;
}

return true;

}

could you please suggest me if anything is wrong here

Posted 3-Aug-17 23:08pm

Member 13089825

Updated 25-Apr-18 21:54pm

Add a Solution

3 solutions

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

OriginalGriff · Answer 1 · 2017-08-03T23:23:00

Look at your regex:

[!/\[]:;|=,+*<>]*

It contains the characters to start and end the "any character in this set" within the set of characters, as well as the Escape character!
Try this:

[!/\\[\]:;|=,+*<>]*

But... that will match no special characters at all - try this:

[!/\\[\]:;|=,+*<>]+

Oh, and you probably need to double each '\' character in your C++ string, so that it doesn't get "swallowed" as the C++ Escape character:

std::regex stringpattern("[!/\\\\[\\]:;|=,+*<>]+");

If you want to use regular expressions, get a copy of Expresso[^] - it's free, and it examines and generates Regular expressions.

Thomas Daniels · Answer 2 · 2017-08-03T23:33:00

There are a few problems with your string:

The backslash inside your character class isn't escaped, so \[ is being treated as escape sequence, but it doesn't exist. And if you'd escape the backslash like \\, so it would 'end up' being a single backslash, the regex will interpret that as 'the next character is meant to be a literal character', so you have to add another backslash, and, in your string, this will look like another double backslash. So for a literal backslash in the regex, you need 4 backslashes in your string.
The ] in the character class ends the character class, but you want it to 'go on', so you have to escape the ]. In regular expression, that would be \], but because you need to escape the backslash in the string, it becomes \\].

So it becomes:

C++

std::regex stringpattern("[!/\\\\[\\]:;|=,+*<>]*");

But we aren't done yet! This code won't do what you want: return false if the string contains one invalid character. The reason is that regex_match matches the full string, whereas you want to search. Instead of regex_match, use regex_search.

And one last thing: the * after the character class means 'zero or more'. That's not what you want: you want 'one or more'. You can replace the * by a + but because you're searching, you can also just remove the *, so your code becomes:

C++

std::regex stringpattern("[!/\\\\[\\]:;|=,+*<>]");

// ...

if (std::regex_search(s_input, stringpattern))
{
    return false;
}
return true;

Jochen Arndt · Answer 3 · 2017-08-03T23:44:00

Solution 3

That is because you forgot to escape the closing square bracket in the character group and that they must be double escaped (so that a backslash is placed in the string to be seen by the regex parser):

wrong:   "[!/\[]:;|=,+*<>]*"
correct: "[!/\\[\\]:;|=,+*<>]*"

You also don't need to convert the input to ANSI when using the wregex class provided by Visual C++:

bool ValidateLoginid(const CString& inputString)
{
    std::wregex stringpattern(L"[!/\\[\\]:;|=,+*<>]*");
    return !std::regex_match(inputString.GetString(), stringpattern);
}

Note also that I have changed the parameter to be a const reference to avoid passing by value and indicate that it is not changed.

There is also no need to use a regular expression if you only want to check if specific characters are present or not. Then just use strstr or CString::FindOneOf.

Posted 3-Aug-17 23:44pm

Jochen Arndt

Updated 3-Aug-17 23:47pm

v2

Comments

Member 13089825 4-Aug-17 6:09am

hi i have tried this,but its not thorwing error when i give test+,test>(if i give combination then its not throwing error)
bool ValidateLoginid(const CString& inputString)
{
std::wregex stringpattern(L"[!/\\[\\]:;|=,+*<>]*");
return !std::regex_match(inputString.GetString(), stringpattern);
}

Jochen Arndt 4-Aug-17 6:20am

As also suggested by others, you should replace the last match char '*' by '+' or '+?'.
I can't actually test it here and have written my solution from mind.

However, I would just use

if (inputString.FindOneOf(_T("!/[]:;|=,+*<>")) >= 0)
// error: string contains unallowed character

Member 13089825 8-Aug-17 7:52am

thank you,its working fine now

Member 13089825 26-Apr-18 6:44am

wrong: "[!/\[]:;|=,+*<>]*"
correct: "[!/\\[\\]:;|=,+*<>]*"
is it possible to validate pattern is correct or not using vc++ mfc

Jochen Arndt 26-Apr-18 6:50am

?You seemed to have stopped typing.

String validation for user input

3 solutions

Solution 1

Solution 2

Solution 3

Add your solution here

Preview 0