c++ use strftime to get a url encoded string?

Question

I want to get the current time in a human reading format, I choose strftime to do this.

The function looks like:

std::string crypto::tools::utc_time_str() {
  time_t nowtime = time(0);
  struct tm mytime;
  gmtime_r(&nowtime, &mytime);
  char buf[32];
  strftime(buf, 32, "%Y-%m-%dT%H:%M:%S", &mytime);
  return buf;
}

It's good, i can get string like this:

2024-08-29T07:25:44

Another requirements is to get it url-encoded. In this case, replace ":" to "%3A" is all I need.

I assume it will be easy.

but seems it can't be done in strftime.

I try the following, all failed:

strftime(buf, 32, "%Y-%m-%dT%H%3A%M%3A%S", &mytime);
2024-08-29T07Thursday28Thursday

strftime(buf, 32, "%Y-%m-%dT%H%\3A%M%\3A%S", &mytime);
2024-08-29T07%A29%A39

I want this function as fast as possible, so, allocate a new string is not a good choice for me.

Can strftime do this?

Answer 1

% is a reserved char and %3A is taken as an invalid sequence. You wanted %%3A.

strftime

%%
  Replaced by %.