giving parameters into math function

Question

If I call in C, math function `"trunc" in math library is define as:

extern double trunc _PARAMS((double));

and in my main file call it:

int i = (int)trunc(2.5);

It works fine, no problems. But if I try to pass double passively, like:

double d = 2.5;
int i = (int)trunc(d);

It won't work?!? In my microprocessor STM32F4 IDE it goes in debugger mode into:

 Infinite_Loop:
 b  Infinite_Loop

and it stuck there. I also change double and try float, int, unit8_t,... no one isn't working. Also other math functions will work fine as I call them like this:

i =  sin(1);
i =  cos(1);

But, it will crashed the same, if called like this:

int a = 1;
i = sin(a);
i = cos(a);

I am running this code on microprocessor STM32F4 Discovery,IDE is Eclipse Ac6.

WedaPashi · Accepted Answer · 2018-05-15T08:25:55.030

If you refer the man page for trunc() you should note that, it says

Link with -lm

So, make sure that you are linking with -lm.

Secondly, when synopsis say double trunc(double x);, there is no point in trying it out with other data types.

If you want to try with other data types then you should look for these variants:

float truncf(float x);
long double truncl(long double x);

Test code:

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

int main(void)
{
    // using trunc function which return
    // Truncated value of the input 
    double d = 2.7;
    printf(" Truncated value is %d \n", (int)trunc(d)); 

    return 0;
}

This generated an output:

 Truncated value is 2

And it was compiled with gcc version 5.3.0

When I compile the same code gcc version 7.2.0 without -lm option, I get following warning:

undefined reference to `trunc'
error: ld returned 1 exit status

giving parameters into math function

1 Answers1