Why am I getting "undefined reference to sqrt" error even though I include math.h header?
The math library must be linked in when building the executable. How to do this varies by environment, but in Linux/Unix, just add -lm
to the command:
gcc test.c -o test -lm
The math library is named libm.so
, and the -l
command option assumes a lib
prefix and .a
or .so
suffix.
You need to link the with the -lm
linker option
You need to compile as
gcc test.c -o test -lm
gcc (Not g++) historically would not by default include the mathematical functions while linking. It has also been separated from libc onto a separate library libm. To link with these functions you have to advise the linker to include the library -l
linker option followed by the library name m
thus -lm
.
This is a likely a linker error.
Add the -lm
switch to specify that you want to link against the standard C math library (libm
) which has the definition for those functions (the header just has the declaration for them - worth looking up the difference.)