I could not found any documentation on why gcc requires -lm for math.h functions but no -l is required for stdio or stdlib functions. Why some functions require the include and the -l gcc command option, and others don't require the -l option? Any thoughts?
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Sourav Ghosh
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Adam Jones
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2I don't know if it's part of the specification, but it's the traditional divide because on old systems the math function would otherwise take up a lot of space when they were not commonly used. – Some programmer dude Feb 04 '19 at 13:41
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The functions in the includes `stdlib.h`, `stdio.h`, etc. almost all live in the same library, libc. – Mad Physicist Feb 04 '19 at 13:47
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It's a bug, and you should complain about it to your vendor. – Steve Summit Feb 04 '19 at 15:30
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There are some libraries which gets linked by default.
One of those default libraries for gcc is libc.a (static) or libc.so (dynamic) (GNU standard C library), and it contains the definition of printf() and scanf() families, including others, prototyped in stdio.h or stdlib.h .
Now, to answer your question, according to the wikipedia article
Under FreeBSD and Linux,[8] the mathematical functions (as declared in
math.h) are bundled separately in the mathematical librarylibm. If any of them are used, the linker must be given the directive-lm.
If you want to check explicitly about the libraries getting linked by deafult, you need to use -v option to check them. You can also pass -Wl,--verbose option to get even more verbose output.
If you want to restrict the default linking, you can make use of -nostdlib switch.
Sourav Ghosh
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