QRegExp in C++ to capture part of string

Question

I am attempting to use Qt to execute a regex in my C++ application. I have done similar regular expressions with Qt in C++ before, but this one is proving difficult.

Given a string with optional _# at the end of the string, I want to extract the part of the string before that.

Examples:

"blue_dog" should result "blue_dog"
"blue_dog_1" should result "blue_dog"
"blue_dog_23" should result "blue_dog"

This is the code I have so far, but it does not work yet:

QString name = "blue_dog_23";
QRegExp rx("(.*?)(_\\d+)?");    
rx.indexIn(name);
QString result = rx.cap(1);  

I have even tried the following additional options in many variations without luck. My code above always results with "":

rx.setMinimal(TRUE);   
rx.setPatternSyntax(QRegExp::RegExp2);

Answer 1

Sometimes it's easier not to pack everything in a single regexp. In your case, you can restrict manipulation to the case of an existing _# suffix. Otherwise the result is name:

QString name = "blue_dog_23";
QRegExp rx("^(.*)(_\\d+)$");
QString result = name;
if (rx.indexIn(name) == 0)
    result = rx.cap(1);

Alternatively, you can split the last bit and check if it is a number. A compact (but maybe not the most readable) solution:

QString name = "blue_dog_23";
int i = name.lastIndexOf('_');
bool isInt = false;
QString result = (i >= 0 && (name.mid(i+1).toInt(&isInt) || isInt)) ? name.left(i) : name;