Why I don't need the flag -lm in MinGW but in Linux I need that explicitly?

Question

If I need to use the math library, I need to add -lm when I'm using GCC in Linux. But on Windows when I'm using GCC in MinGW-w64, I didn't use -lm and it works well.

I know the reason why it is necessary to link libm. But I don't really know why I can omit that in Windows?

It's just a configuration difference. gcc driver with Mingw is configured to link in the math library by default, gcc in linux is not. — Peter, Jan 07 '18 at 04:21
FWIW, you don't need to specify `-lm` on a Mac, either. There's no harm done if you do, but likewise no harm done if you don't. — Jonathan Leffler, Jan 07 '18 at 05:33

score 7 · Accepted Answer · answered Jan 07 '18 at 05:20

7

Because, under MinGW, the math functions aren't actually defined in libm. "libm" is an empty library used as a placeholder; the math functions are actually defined in MSVCRT.DLL, which MinGW uses as its standard library.

(The validity of using the system's MSVCRT as a standard C library is debatable. Nevertheless, that's what MinGW does.)

answered Jan 07 '18 at 05:20

1

Is there a way to use the `libm` optimized math on `MinGW64`? – Royi Sep 23 '20 at 18:40

Steve Summit · Answer 2 · 2018-01-07T14:50:42.677

1

In my opinion, it is a significant, longstanding bug in the Unix and Linux C library setup that you actually need to use -lm. I'd say you should thank MinGW for fixing this.

edited Jan 07 '18 at 14:50

answered Jan 07 '18 at 12:51

Steve Summit

45,437
7
70
103

Why I don't need the flag -lm in MinGW but in Linux I need that explicitly?

2 Answers2