Problem compiling Math. h

Question

Good evening, when I try to use some function of Math. h and put as argument a variable and try to compile I get an error. Can you explain to me why this is happening?

Follow an example code:

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

int main(){

    int cacheSize = 4;
    int memSize = 16;

    // log de cacheSize na base 2
    double cacheBits = 0;
   cacheBits = log(cacheSize)/log(2);

   // log de memSize na base 2
   double memBits = 0;
   memBits = log(memSize)/log(2);

   return 0;
}

The error message I get:

gcc teste.c -o teste

/usr/bin/ld: /tmp/ccHF5avR.o: na função "main":
teste.c:(.text+0x25): referência não definida para "log"
/usr/bin/ld: teste.c:(.text+0x51): referência não definida para "log"
collect2: error: ld returned 1 exit status

Answer 1

If you get this error it is because the implementation of the Math library is not being linked in the process. To resolve add the -lm in the compilation instruction:

gcc teste.c -o teste -lm

When it includes the math.h includes the definition of functions but not their implementations, which is why you see this error.