Question

How to test if a number stored as string an exponential number (in Linux)?

I can use methods like scanning the numbers and finding if there exists an ‘e’, but i need a smarter way to find out.

Does there exist any API to quickly find out and tell if it is an exponential number?

I can use brute force approach like searching through the entire string, and getting a single ‘e’ followed by a +/- and then a number. But i need a quicker and smarter way, which consumes less machine cycles.

P.S: Exponential numbers are numbers like: 43e4, 23e-2 (any number with an e in between)

Answer 1

regex_t re;
regcomp(&re, "^([0-9]+[.]?[0-9]*|[0-9]*[.][0-9]+)[eE][+-]?[0-9]+$", REG_EXTENDED);
if (!regexec(&re, str, 0, 0, 0)) /* It's an "exponential number" */