Sometimes C is inappropriate (eg you'd be nuts to build a website in C yet some sites do offer real time services)
Often the data set and/or logic required makes C an inappropriate language (eg you wouldn't use C for AI nor for some types of database operations).
And even in the cases where you're just building a standard procedural system, sometimes the interface lends itself better to other languages (eg C would be possibly the worst language for real time websites.)
But even in the cases where you're building a solution that's suited for C, there are still other performance languages which could be used.
"Real time" is quite a general term and as such, sometimes it makes more sense to use scripting languages which are performance tuned. Which is where writing 'good' PCRE is critical as RegEx can be optimised and compiled - if you understand the quirks of the language well enough to avoid easy pitfalls, eg s/^\s//; s/\s$//; outperforms s/(^\s|\s$)//; despite it being two separate queries as opposed to one.
If you're in a situation where the overhead of a couple of function calls is unacceptable, regexes are totally unacceptable and you need to write custom character manipulation.
This situation is really rare and in almost all business cases, using C is inappropriate.