ESP32 Forum

Posted: **Sun Jan 16, 2022 9:08 pm**

I'm trying to parse an MQTT topic that may contain variables. Regex seems like the easiest solution here. But the C API of regex seems like a PITA. I followed the manpage and examples from the web, but the compiler rejects it.

Code: Select all

regex_t ledRegex;
regcomp(&ledRegex, "^/led/ch/([0-9]+)/([a-z]+)", 0);

regmatch_t match[3];
if (regexec(&ledRegex, topic, 2, NULL, 0) == 0)
{
	char* p1 = strndup(event->topic + match[1].rm_so, match[1].rm_eo - match[1].rm_so);
	char* p2 = strndup(event->topic + match[2].rm_so, match[2].rm_eo - match[2].rm_so);
	printf("LED topic parsed: ch=%s cmd=%s\n", p1, p2);
	//uint16_t num = strtol(data, NULL, 10);
	free(p1);
	free(p2);
}

This is the error:
error: 'match[1].rm_so' may be used uninitialized in this function [-Werror=maybe-uninitialized]
It's repeated for every access of that structure.

Should I stop regarding compiler warnings? In the past 15 years of coding in C# I managed to resolve all warnings, many of them pointed me to real problems and needed fixing. Not sure how C handles this.

I'm using VSCode and the esp-idf extension.

Posted: **Sun Jan 16, 2022 9:26 pm**

More trouble.

For an ugly quick fix, I added this to convince the compiler that it's okay:

Code: Select all

match[1].rm_so = 0;
match[1].rm_eo = 0;
match[2].rm_so = 0;
match[2].rm_eo = 0;

But the code doesn't match the input "/led/ch/0/temp". The return value is REG_NOMATCH. regcomp() returned 0 which is good.

If I pass the REG_EXTENDED flag to regcomp, it still returns 0 but regexec crashes the application and reboots.

Should I roll my own string parsing instead of fighting the regex functions that the code editor doesn't even know? This line is underlined:

Code: Select all

#include <regex.h>

with the message: The include file was not found in "browse.path" (message translated by me)

Posted: **Sun Jan 16, 2022 10:18 pm**

Try "^/led/ch/\\([0-9]\\+\\)/\\([a-z]\\+\\)"

Posted: **Mon Jan 17, 2022 9:48 am**

WiFive wrote: ↑
Sun Jan 16, 2022 10:18 pm
Try "^/led/ch/\\([0-9]\\+\\)/\\([a-z]\\+\\)"

Are you sure what that means? I don't want to escape the control characters, I want them to work. There are no parentheses and plus signs in my data to match.

ESP32 Forum

Regex code example without "uninitialized" warnings?

Regex code example without "uninitialized" warnings?

Re: Regex code example without "uninitialized" warnings?

Re: Regex code example without "uninitialized" warnings?

Re: Regex code example without "uninitialized" warnings?