How to fix GCC undefined reference to `sqrt'

Problem:

When trying to compile your application using gcc, you see an error message like

how-to-fix-gcc-undefined-reference-to-sqrt.txt

/usr/bin/ld: /tmp/ccxPIowU.o: in function `run_mymath':
mathstuff.c:(.text+0x15d): undefined reference to `sqrt'

/usr/bin/ld: /tmp/ccxPIowU.o: in function `run_mymath':
mathstuff.c:(.text+0x15d): undefined reference to `sqrt'

Solution

You need to link the math library using the -lm flag (-lxxx means: “link the xxx library”, i.e. -lm means “link the m” library)

For example, instead of

gcc -o myprogram *.c

gcc_link_math.sh

gcc -o myprogram *.c

gcc -o myprogram *.c

use

gcc -o myprogram *.c -lm

gcc_link_math_with_lm.sh

gcc -o myprogram *.c -lm

gcc -o myprogram *.c -lm

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