I want to make a simple function involving sqrt(), floor() and pow(). So, I included <math.h>. When I try to use my function, my program says that sqrt() and floor() do not exist. I've triple checked my files and rewritten them, but it still gives the same error. Just to check if there was anything wrong with the <math.h> directory, I made another separate file that calculated the same thing and it worked. I am clueless right now. What am I doing wrong?
The code of the non functioning program:
#include <math.h>
#include "sumofsquares.h"
int sumofsquares(int x){
int counter = 0;
int temp = x;
while(temp != 0){
temp = temp - (int)pow(floor(sqrt(temp)), 2);
counter ++;
}
return counter;
}
The working test file:
#include <stdio.h>
#include <math.h>
int main(void){
printf("%d", (int)pow(floor(sqrt(3)), 2));
}
the error is this
/tmp/ccm0CMTL.o: In function sumofsquares':
/home/cs136/cs136Assignments/a04/sumofsquares.c:9: undefined reference
to sqrt' /home/cs136/cs136Assignments/a04/sumofsquares.c:9: undefined
reference to floor' collect2: ld returned 1 exit status`
I am using runC on a virtual Ubuntu OS to compile
You're probably missing the -lm argument to gcc, required to link the math library. Try:
gcc ... <stuff> ... -lm
There are at least two C FAQs relevant to your problem:
14.3
13.26
Related
Why does this compile and run this w/o the "-lm" switch on gcc:
#include <stdio.h>
#include <math.h>
int main()
{
printf("2 to the 8th power is %f\n",pow(2.0,8.0));
return(0);
}
but this:
#include <stdio.h>
#include <math.h>
int main()
{
float a,b;
a = 2.0;
b = 8.0;
printf("2 to the 8th power is %f\n",pow(a,b));
return(0);
}
gives the error:
undefined reference to `pow'
unless you link the math library with -lm
The behavior is the same if I use doubles rather than floats. Is there some sort of rudimentary pow() function hidden in standard library, or is the linker just resigned to working with idiots and links the math library for really simple cases?
I'm using gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0 if that makes any difference. It's not a big deal, just curious why that happens, thanks!
I had myself, a problem of understanding, what is wrong with the above. I got the same behaviour with gcc -O0. Running executable with strace and gdb showed that no function call made at all.
Scratched my head, read some comments and got it. Me alone, would have guessed the answer for hours. All credits goes to commenters
Try to change your code to
....
double t = (int)(2.0 + 1.0) % 2 + 1.0;
double r = pow(2.0+t,8.0);
....
With -O0 flag you should hopefully get undefined reference to 'pow' message.
#include <stdio.h>
#include <math.h>
int exp_for_level(int n) {
return (int)(100 * pow(n, 2.3));
}
int main(){
int x;
x = exp_for_level(6);
printf("%d", x);
return 0;
}
I receive the following error when I run this code on an online compiler
/tmp/cc28S7ML.o: In function exp_for_level':
main.c:(.text+0x19): undefined reference to `pow'
collect2: error: ld returned 1 exit status
How do I rectify this?
After I couldn't get it to work on the online compiler, I followed advice from some other threads on
The file is stored under a file grades.c on my mac
I've tried entering this
$ gcc - Wall - lm -o grades grade . c
into my terminal and i just get zsh error: command not found
Any ideas on what the issue is here too?
The online compiler I'm using is
https://www.tutorialspoint.com/compile_c_online.php
EDIT: in my post, in main I'd miswritten the function as exp_to_level instead of exp_for_level. Didn't copy paste the entire code as it's too long. I narrowed it down and retyped it to the portion that yields the error.
There are some errors in your code, you have defined a function exp_for_level but you use exp_to_level.
Then your x variable is not defined
If you fix your code like this:
#include <stdio.h>
#include <math.h>
int exp_for_level(int n) {
return (int)(100 * pow(n, 2.3));
}
int main(){
int x = exp_for_level(6);
printf("%d", x);
return 0;
}
and you compile:
gcc -Wall powtest.c -o powtest -lm
it works.
About the error on the online compiler:
The undefined reference error occurs because you are missing -lm linker option.
Edit the online compiler command clicking on Project->Compile Options:
About this problem on your local machine:
After I couldn't get it to work on the online compiler, I followed
advice from some other threads on The file is stored under a file
grades.c on my mac I've tried entering this
$ gcc - Wall - lm -o grades grade . c
into my terminal and i just get zsh error: command not found
you don't have the compiler installed.
You should install clang, Have a look to this question
First of all your function name is wrong in the main take a look here exp_for_level
and in main its exp_to_level change one of them then also add int x in main to solve the issue.
I have this code which I'm trying to run with GCC-TDM 1.7.4-2 using -msse4.2 (I tried msse4) with an error:
sse_lzcnt.c|7|warning: implicit declaration of function '__lzcnt16'|
sse_lzcnt.c|9|warning: too many arguments for format|
obj\Debug\sse_lzcnt.o||In function `main':|
sse_lzcnt.c|7|undefined reference to `__lzcnt16'|
An undefined reference is usually a linking error due to a missing lib file (.a ending) but the intrinsics headers don't need one?
I made sure the intrinsics headers are in the correct include directory. Heres the code,
#include <x86intrin.h>
#include <stdio.h>
int main()
{
unsigned short __X = 256;
unsigned short RESULT = __lzcnt16(__X);
printf("result: ", RESULT);
return 0;
}
You need to use the gcc command line option: -mlzcnt
I have a strange problem with fabs function in C code. I have two double values and I want to find the absolute value of their difference using code like this:
a = 87.967498;
b = 218.025015;
if (fabs(a-b)<2.0)
...code to execute
The value of fabs(a-b) is an int and is equal to 1. I don't know whats the problem here and I can't find anything on the net. Any help would be great!!
You didn't include <math.h>. Add the following line to your other includes:
#include <math.h>
In order to find such errors easier I recommend you to use verbose compiler warnings (gcc -Wall -Wextra ... if you use gcc).
The only way that fabs could return an int is either:
Your program uses a declaration of fabs other than the version declared in math.h.
Your program failed to include math.h and so does not declare fabs at all. In which case parameters and return values default to int. Which is of course an error because the actual implementation of fabs does not match and so the value returned is nonsense.
See this code:
#include <math.h>
#include <stdio.h>
int main()
{
float a = 87.967498;
float b = 218.025015;
float diff = a-b;
printf("diff=%f\nfabs(diff)=%f\n",diff,fabs(diff));
if (fabs(diff)<2.0) {
printf("OK\n");
} else {
printf("FAIL\n");
}
return 0;
}
It produces this output:
diego#malti:~/tmp$ clang test-math.c -o test-math -lm
diego#malti:~/tmp$ ./test-math
diff=-130.057510
fabs(diff)=130.057510
FAIL
See? The application is OK, the diff (218-87=130), which is not smaller then 2.
See also then when I am compile, I also link -lm to get the mathematical library. The same syntax applies for gcc, I just love using clang :)
pow doesn't accept the second parameter to be a variable on gcc
The following code works fine on VC++10
// file test.cc
#include "stdafx.h"
#include <stdio.h>
#include <math.h>
int main(void)
{
double x = 10;
int y = 20;
printf("%f\n", pow(x, y));
return 0;
}
But the following code doesn't not work on gcc:
// test.c
#include <stdio.h>
#include <math.h>
int main(void)
{
double x = 10;
int y = 20;
printf("%f\n", pow(x, y)); // error here, says no such function, however when pass the second argument in `pow` for the code runs by gcc, It works fine!
return 0;
}
You're mistaken. It has nothing to do with the second parameter.
In POSIXish systems pow() is in libm, whereas in win32ish systems it is part of the standard C library. That means instead of this:
$ gcc program.c
/tmp/ccTw1gCA.o: In function `main':
program.c:(.text+0x30): undefined reference to `pow'
you need to do this:
$ gcc program.c -lm
The reason it may appear that the second parameter works as a constant but not as a variable is that gcc has a built-in implementation of pow(). If the second parameter is a constant it might be using that where if it's a variable it's falling back on the glibc pow() function. See:
http://gcc.gnu.org/onlinedocs/gcc-4.5.0/gcc/Other-Builtins.html#Other-Builtins
If you pass -fno-builtin to gcc you should see consistent behavior--in this case error messages no matter what you pass to pow(). As others have mentioned whenever you use anything out of math.h you need to link with -lm.