I'm an absolute beginner to C and I've read a few books but never really played with it. I'm starting to try to apply what I've read with a very simple program that returns the sin of a number. The hardest thing I've encountered with C is knowing how and when to use pointers.
I'm sure this is simple but here is how I've written my test:
#include <stdio.h>
#include <math.h>
int main(void)
{
double x;
printf("Enter a number to calculate the sin(x): \n");
scanf("%lf", &x);
printf("sin(%lf) = %lf\n", x, sin(x));
return 0;
}
I'm compiling and executing this code in Ubuntu
gcc -lm sinCalc.c && ./a.out
Error I'm receiving is this:
/tmp/blaha.o: In function `main':
sinCalc.c:(.text+0x31): undefined reference to `sin'
collect2: ld returned 1 exit status
Undefined symbols are resolved left to right, so
gcc sinCalc.c -lm && ./a.out
should work.
Are they [structs] like an interface in Java?
No. Structs are an aggregate of a number (1 or more) of types that can be dealt with as a single unit in certain circumstances (assignment, parameter passing).
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.
This question already has answers here:
Why do you have to link the math library in C?
(14 answers)
Closed 4 years ago.
Just starting to learn C, and I found this example program on a C tutorial website, and it is giving an error upon compiling.
Here is the program, calculates the square root of a number based on user input:
#include <stdio.h>
#include <math.h>
int main()
{
double num, root;
/* Input a number from user */
printf("Enter any number to find square root: ");
scanf("%lf", &num);
/* Calculate square root of num */
root = sqrt(num);
/* Print the resultant value */
printf("Square root of %.2lf = %.2lf", num, root);
return 0;
}
I compile it using gcc in Ubuntu:
gcc -o square_root square_root.c
And here is the error:
/tmp/cc9Z3NCn.o: In function `main':
square_root.c:(.text+0x4e): undefined reference to `sqrt'
collect2: error: ld returned 1 exit status
What am I doing wrong? I can see that the math module is imported, so why the error?
Again, I just started studying C today, and I just want to figure out how to get programs to run. Thank you for your patience as it must be something obvious.
sqrt lives in the math library, so you need to tell your program to link to it with -lm:
gcc -o square_root square_root.c -lm
You need to compile it with -lm flag
gcc -o square_root square_root.c -lm
I'm trying to set a function pointer to point to the pow function.
Here's my code:
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
int main(void){
double (*func)(double, double) = pow;
return 0;
}
But the program doesn't compile.
I get this error:
$ gcc test.c -o test
/tmp/ccD6Pmmn.o: In function `main':
test.c:(.text+0x8): undefined reference to `pow'
collect2: error: ld returned 1 exit status
I'm using Ubuntu 15.10.
Anyone knows what's wrong with my code?
Thanks
You need to compile with -lm via command line or configure your IDE to add it into the linking process. This is due to the fact that some libraries are pretty large and to avoid taking up space in your program and compilation time, this was setup at the beginning of C when computers were much slower and would take MUCH more to compile and a matter of space was CRUCIAL.
I am trying to write a program to approximate pi. It basically takes random points between 0.00 and 1.00 and compares them to the bound of a circle, and the ratio of points inside the circle to total points should approach pi (A very quick explanation, the specification goes in depth much more).
However, I am getting the following error when compiling with gcc:
Undefined first referenced
symbol in file
pow /var/tmp//cc6gSbfE.o
ld: fatal: symbol referencing errors. No output written to a.out
collect2: ld returned 1 exit status
What is happening with this? I've never seen this error before, and I don't know why it's coming up. Here is my code (though I haven't fully tested it since I can't get past the error):
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
int main(void) {
float x, y;
float coordSquared;
float coordRoot;
float ratio;
int n;
int count;
int i;
printf("Enter number of points: ");
scanf("%d", &n);
srand(time(0));
for (i = 0; i < n; i++) {
x = rand();
y = rand();
coordSquared = pow(x, 2) + pow(y, 2);
coordRoot = pow(coordSquared, 0.5);
if ((x < coordRoot) && (y < coordRoot)) {
count++;
}
}
ratio = count / n;
ratio = ratio * 4;
printf("Pi is approximately %f", ratio);
return 0;
}
use -lm during compilation(or linking) to include math library.
Like this: gcc yourFile.c -o yourfile -lm
need to Link with -lm.
gcc test.c -o test -lm
The error is produced by the linker, ld. It is telling you that the symbol pow cannot be found (is undefined in all the object files handled by the linker). The solution is to include the library which includes the implementation of the pow() function, libm (m for math). [1] Add the -lm switch to your compiler command line invocation (after all the source file specifications) to do so, e.g.
gcc -o a.out source.c -lm
[1] Alternatively, you could have your own implementation of pow() in a separate translation unit or a library, but you would still have to tell the compiler/linker where to find it.