How do I perform regex based string manipulation with a C++03 constraint and no external libraries?

Question

I have some string which I need to manipulate to be lowercase and replace some characters to blanks using regex.

The Java equivalent is:

str.toLowerCase();
str.replaceAll("[^a-z]", "");
str.replaceAll("\\s", "");

Within a c++03 constraint, and without using Boost or another library, how can I achieve the same functionality in C++? The version of g++ the server I am running on is 4.8.5 20150623.

Lowercasing is simple:

char asciiToLower(char c) {
    if (c <= 'Z' && c >= 'A') {
        return c - ('A' - 'a');
    }
    return c;
}

std::string manipulate(std::string str) {
    for (std::string::iterator it = str.begin(); it != str.end(); ++it) {
        it = asciiToLower(it);
    }
}

But what about the other two?

Are you asking how to do a substitution regex in C++11? Plenty of existing resources on that topic. Did you have some specific issue? — Lightness Races in Orbit, Oct 27 '19 at 19:59
You said "within with a C++0x restriction". If that doesn't mean "in C++11", what does it mean instead? — Lightness Races in Orbit, Oct 27 '19 at 19:59
@LightnessRacesinOrbit using `-std=c++0x` compiler flag instead of `-std=c++11`. The server I am working on supports the former but not the latter. — gator, Oct 27 '19 at 20:00
@gator: So, you want to use pre-standard, experimental, preview C++11 mode (that's what `-std=c++0x` means) in some compiler. You're going to have to tell us, then, what that compiler is. I mean the exact version. — Lightness Races in Orbit, Oct 27 '19 at 20:01
@LightnessRacesinOrbit I'm making an assumption of c++03, I'll make an edit to my post. — gator, Oct 27 '19 at 20:02

score 2 · Accepted Answer · answered Oct 27 '19 at 20:03

2

C++03 does not support regular expressions. This was introduced in C++11.

So, without (a) external libraries, or (b) writing a regex engine yourself, you can't.

However, GCC has regex support from 4.9, in the experimental -std=c++0x mode. So, if you can flip into that, and your GCC is new enough, maybe that can help you.

(Don't be misled into thinking that GCC 4.8 supports it: it doesn't; it's lying.)

Otherwise I suggest you update your compiler. Even C++11 is old now.

answered Oct 27 '19 at 20:03

Lightness Races in Orbit

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Waiting for some smart alec to point out that you could do a `system()` call to the shell and get some OS utility to do it, then parse the response. I'm not counting that as a C++ solution. – Lightness Races in Orbit Oct 27 '19 at 20:05
Wouldn't work anyway. How would you extract the result? ``system`` only returns an int. This would require eg.: using external files to perform all processing. – Luis Machuca Oct 30 '19 at 15:47
@LuisMachuca Yep, the shell command could pipe the result to a file, then the C++ program could open the file to read it back in. Don't laugh: I've seen people do this crap in production. – Lightness Races in Orbit Oct 30 '19 at 17:07

How do I perform regex based string manipulation with a C++03 constraint and no external libraries?

1 Answers1