ESP8266 ISO 8601 string to tm struct

Question

I have a web service that returns timestamps in ISO 8601 format, e.g., "2021年06月25日T12:00:00" I'm trying to turn the timestamp string into a tm type struct from the ESP8266 library <time.h>, to perform time calculations using the difftime() function.

I've been referring to the Redhat time functions https://sourceware.org/newlib/libc.html#time, as it seem to be compatible with the ESP library, though all i can find are functions converting tm structs to timestamp strings. Are there any functions to convert a string timestamp into a tm struct and then back into epoch? Or what would be the best way to approach this kind of conversion on the ESP8266 platform?

• Juraj: Does this answer your question? How to parse 20180810T143000Z to time_t
• Boyfinn: Thank you! This method works too, though i find the answer below to be more useful.
• Juraj: sorry yes, there is a different format. strptime can't parse a timestamp without delimiters.

Answer 1

Try strptime from the time.h.

void setup()
{
 
 struct tm tm = {0};
 char buf[100];
 
 // Convert to tm struct
 strptime("2001年11月12日 18:31:01", "%Y-%m-%d %H:%M:%S", &tm);
 
 // Can convert to any other format
 strftime(buf, sizeof(buf), "%d %b %Y %H:%M", &tm);
 Serial.printf("%s", buf);
}
void loop()
{
 yield();
}

• Boyfinn: Thank you. The method above works. I just formatted my string as "%Y-%m-%dT%H:%M:%S",instead.