This should be short. I've been writing some code and decided to see if it was C99 compliant. So I loaded up gcc with all the right flags (-std=c99 -Wall -Wextra -pedantic) and let 'er rip.
Huh? What do you mean strdup() is implicitly defined? I'm including string.h!
Well, fancy that. Learn something new every day. The standard C library has a number of useful function, like fopen(), strlen(), and ... not strdup(). Note I said "standard" there. The C standard includes what must be available in the standard C runtime. And the strdup() function is not one of them.
Sure, lots of runtimes have it - glibc has had it for I-don't-know how long. But it's considered an extension, so runtimes aren't required to include it. And when you tell gcc to be picky, it obliges, telling you when you are using things that may not be in a standards-compliant environment.
Now that is not to say that strdup() isn't in *any* standard. It is in POSIX. So a POSIX-compliant runtime will have it. But you can be C99 compliant but not POSIX compliant.
The latest C standard, C23, does include it. And it hasn't changed, so you don't have to re-write all your code. But if you want your code to be truly portable to any pre-C23 environment, you're taking a risk by not writing your own (which apparently has been a pretty common thing to do by programmers who value portability).
