C linker error with gcc and math.h

Question

I am getting an error stating pythagorean.so: undefined symbol: cos . I am compiling with the math.h , stdlib.h , and stdio.h libraries and the -lm switch. Here a code snippet:

static bool
law_of_cosine_run(esh_command* cmd)
{
    if (strcmp(cmd->argv[0], "lawofcosine") == 0) {
        printf("The length of the third side is: %f\n", 
        law_of_cosine(strtol(cmd->argv[1], NULL, 10), 
        strtol(cmd->argv[2], NULL, 10), strtol(cmd->argv[3], NULL, 10)));       
        return true;
    }
    return false;
}

static double
law_of_cosine(double x, double y, double z)
{
    return sqrt((x * x) + (y * y) - (2 * x * y * cos(z)));
}

Does anyone know why this would occur? pythagorean.c is my .c file.

Thanks

Answer 1

编译时，请确保您键入

gcc *.c -lm