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.
Related
#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 was trying today to check an Answer and I realized that if i use codeblocks (with gcc) i have to treat the error different from the command line (Ubuntu Linux) using gcc.
The program is like this:
#include<stdio.h>
#include<math.h>
int main(void){
double len,x,y =0;
int n=123456;
len=floor(log10(abs(n))) + 1;
x = n / pow(10, len / 2);
y = n - x * pow(10, len / 2);
printf("First Half = %f",x);
printf("\nSecond Half = %f",y);
return 0;
}
And if i try to compile it i get:
error: implicit declaration of function ‘abs’ [-Werror=implicit-function-declaration]|
So here is the funny thing. I added -lm to the Compiler => global compiler => settings => Other settings, but the result is the same.
It is working only if i include stdlib.h.
#include<stdio.h>
#include<stdlib.h>
#include<math.h>
int main(void){
double len,x,y =0;
int n=123456;
len=floor(log10(abs(n))) + 1;
x = n / pow(10, len / 2);
y = n - x * pow(10, len / 2);
printf("First Half = %f",x);
printf("\nSecond Half = %f",y);
return 0;
}
But if I use command line (in terminal) using the comand:
gcc program.c -o program -lm
The program compiled successfully.
My question: Why happens this ?
I did a research on interent and found that some people says the abs function is declared in stdlib.h, not math.h. but if i compile in command line (without including stdlib.h) with -lm works. I'm confused.
Short answer: Try
gcc -Wall -Wextra -pedantic -o program -lm
or
gcc -Wall -Wextra -Werror -pedantic -o program -lm
to make it fail on warnings as Codeblocks seems to do.
Long answer: Linking to a library is a completely different matter than including a header file. In C, for historic reasons, it is "allowed" to use a function that is not declared. The compiler in this case assumes a function returning int and taking whatever arguments you give it. For abs(), these assumptions hold. So later, the linker finds the function when linking with libm and everything is fine.
But there are quite some catches: First you will miss simple typos if you don't enable warnings. Second, the compiler is unable to check the arguments you give -> crashing program ahead. And even more problems are to expect if the function does return something other than int.
abs() is declared in stdlib.h. To use it, include this header. And always enable compiler warnings (Codeblocks obviously does it for you).
This question already has answers here:
gcc will not properly include math.h
(2 answers)
Closed 8 years ago.
I'm trying to learn enough c to satisfy my occasional need to write simple programs that answer specific questions I have. I've been following a tutorial and using Geany for ease of use. Instead, I can't seem to get the simplest program to run. Here is my source code:
#include <stdio.h>
#include <math.h>
int main(int argc, char **argv)
{
int x, y;
double c, sqr_c;
for (x = 10; x <= 31; x++)
{
for (y = 10; y <= 31; y++)
{
c = 1000 * x * x + y * y;
sqr_c = sqrt(c);
printf ("%f\n", sqr_c);
}
}
return 0;
}
It compiles fine (gcc -c) but when I try to build an executable, I get:
gcc "concsqr.c" -Wall -o "concsqr" (in directory: /home/chip)
/tmp/cccSmdZS.o: In function `main':
concsqr.c:(.text+0x4b): undefined reference to `sqrt'
collect2: error: ld returned 1 exit status
Compilation failed.
I read something about making sure the linker can locate the library where sqrt() is defined, but I do not know how to do that, and wouldn't it be in a standard location anyway? Why doesn't the linker already know where it is? It's a standard library for c.
You must try to compile your program with the -lm flag as libm.so is the math library, and the -l flag adds a lib prefix and .a or .so suffix.
gcc concsqr.c -Wall -o concsqr -lm
I was testing the cblas ddot, and the code I used is from the link and I fixed it as
#include <stdio.h>
#include <stdlib.h>
#include <cblas.h>
int main()
{
double m[10],n[10];
int i;
int result;
printf("Enter the elements into first vector.\n");
for(i=0;i<10;i++)
scanf("%lf",&m[i]);
printf("Enter the elements into second vector.\n");
for(i=0;i<10;i++)
scanf("%lf",&n[i]);
result = cblas_ddot(10, m, 1, n, 1);
printf("The result is %d\n",result);
return 0;
}
Then when I compiled it, it turned out to be:
/tmp/ccJIpqKH.o: In function `main':
test.c:(.text+0xbc): undefined reference to `cblas_ddot'
collect2: ld returned 1 exit status
I checked the cblas file in /usr/include/cblas.h, and noticed there is
double cblas_ddot(const int N, const double *X, const int incX,
const double *Y, const int incY);
I don't know where it is going wrong. Why does the compiler said the "cblas_ddot" is undefined reference?
You can't just include the header - that only tells the compiler that the functions exist somewhere. You need to tell the linker to link against the cblas library.
Assuming you have a libcblas.a file, you can tell GCC about it with -lcblas.
The web site for GNU Scientific Library tells you how to do this:
2.2 Compiling and Linking
My problem was just solved. The reason is that I made a mistake when inputed the link path. Thanks for Jonathon Reinhart's answers, they are really helpful when learning how to code in linux.
The compile commands are:
gcc -c test.c
gcc -L/usr/lib64 test.o -lgsl -lgslcblas -lm
Where "/usr/lib64" is the correct link path.
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).