sqrtf undefined reference to `sqrtf' in c

问题

Hello i am using linux 12.04 and geany for coding. The code i am writing in C worked completely fine until i used the sqrtf command to find the square root of a float. Error: HAC3.c:(.text+0xfd7): undefined reference to `sqrtf' .

The part of code i am using sqrtf:

float syn(float *a, float *b, int dimensions)
{
    float similarity=0;
    float sumup=0;
    float sumdown=0;
    float as=0;
    float bs=0;
    int i;
    for(i=0; i<dimensions; i++)
    {
        sumup = sumup + a[i] * b[i];
        as = as + a[i] * a[i];
        bs = bs + b[i] * b[i];
    }
    sumdown = sqrtf(as) * sqrtf(bs);
    similarity = sumup / sumdown;
    return similarity;
}

I included math.h but this doesn't seem to be the problem. So i am wondering is there any way to fix geany so this won't come up again? I've got little knowledge so try to explain if possible.

回答1:

Go to Build -> Set Build Commands then under C commands click on the empty label and it will let you specify a new label (name it Link). Type in it gcc -Wall -o "%e" "%f" -lm - where -lm will tell it to link the math library to your app. Click OK.

Then click on Build and select your newly created label - Link. This should do it for you.

回答2:

You need to link with -lm to provide the math functions.

回答3:

In addition to the many fine answers here, the portable form of the command that supports C99 version of <math.h> is specified by POSIX as c99 -l m. That having been said, every important Linux compiler supports -lm.

来源：https://stackoverflow.com/questions/16974669/sqrtf-undefined-reference-to-sqrtf-in-c