a gcc sqrt function bug?

Question

The following program cannot compile in gcc. But it compiles OK with g++ and MSC++ with .c extension.

#include <math.h>
#include <stdio.h>

int main()
{
  double t = 10;
  double t2 = 200;

  printf("%lf\n", sqrt(t*t2));

  return 0;
}

My system is CentOS, the version info.

> gcc --version
gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-46)
Copyright (C) 2006 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

The error info:

> gcc test.c
/tmp/ccyY3Hiw.o: In function `main':
test.c:(.text+0x55): undefined reference to `sqrt'
collect2: ld returned 1 exit status

Is this a bug?

Any one can do a test for me?

See also http://stackoverflow.com/questions/1033898 – ephemient Dec 31 '09 at 23:41 — ephemient, Dec 31 '09 at 23:41

score 18 · Accepted Answer · answered Dec 30 '09 at 17:20

18

Have you linked the math library?

gcc -lm test.c -o test

answered Dec 30 '09 at 17:20

Tom

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6

Because `g++` pulls in `-lstdc++` which pulls in `-lm`. – ephemient Dec 30 '09 at 17:55
2

You don't want to compile 'raw' C code with `g++`. C and C++ are different languages. – Alok Singhal Dec 31 '09 at 06:35
2

The gcc I use requires the `-lm` *after* test.c (4.6.1 on Ubuntu) – nickd Dec 07 '11 at 14:36

Prasoon Saurav · Answer 2 · 2009-12-30T17:35:06.493

2

Try gcc -lm test.c -o test

For gcc, you need to tell it to link the math library in, by adding -lm to your gcc call.

edited Dec 30 '09 at 17:35

answered Dec 30 '09 at 17:21

Prasoon Saurav

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score 2 · Answer 3 · answered Dec 30 '09 at 17:21

2

Add the math library with flag -lm

> gcc test.c -lm

answered Dec 30 '09 at 17:21

Drew Dormann

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score 2 · Answer 4 · answered Jun 08 '17 at 08:35

2

The thing is, gcc -lm test.c -o test won't work because gcc will treat the -lm as a compiler and not a linker option. You need to put the -lm at the end of the command instead, i.e. gcc -o test test.c -lm

answered Jun 08 '17 at 08:35

user36870

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smilinggoomba · Answer 5 · 2011-08-01T11:56:36.590

2

Everybody has been saying this, but I will too. You have to "tell" gcc to link to the math library. When you compile, instead of saying gcc test.c, you have to say gcc -lm test.c. I wish that I could just #include math.h and not have to do anything else.

edited Aug 01 '11 at 11:56

answered Aug 01 '11 at 11:43

smilinggoomba

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a gcc sqrt function bug?

5 Answers5