Append -lm to the end of your gcc command.
With all recent versions of GCC on GNU/Linux systems like Ubuntu, when you use the math library, you have to explicitly link to it. It is not automatically linked to along with the rest of the standard C library.
If you are compiling on the command-line with the gcc or g++ command, you would accomplish this by putting -lm at the end of the command.
For example: gcc -o foo foo.c -lm
Append -lm to the end of your gcc command.
With all recent versions of GCC on GNU/Linux systems like Ubuntu, when you use the math library, you have to explicitly link to it. It is not automatically linked to along with the rest of the standard C library.
If you are compiling on the command-line with the gcc or g++ command, you would accomplish this by putting -lm at the end of the command.
For example: gcc -o foo foo.c -lm
If you are going to compile a C program with math.h library in LINUX using GCC or G++ you will have to use –lm option after the compile command.
gcc xyz.c -o xyz -lm
Here,
gcc is compiler command (compiler name)
xyz.c is a source file name.
-o is an option to specify the output file.
xyz is the name of the output file.
-lm is an option to link againt the math library (libm).
for more details here is the link containing complete article on it.
Compiling C program with math.h in Linux.
Is #include <math.h> necessary?
gcc - C Failing to compile: Can't find math.h functions - Stack Overflow
compilation - Why do you have to link the math library in C? - Stack Overflow
C89 help importing math functions from a text file.
There's no "execute this as if it were code" in C because C is a compiled language- there's nothing that understands C code at run time. You need to write a parser to split each equation up into parts and then write code to handle each math operation.
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So I started to study C and noticed something interesting.
TL;DR:
Building the code gives me a warning/error, telling me to declare the function or to include math.h. But I can ignore that message and still run the code and the function gets executed. I build the code by using gcc code_name.c -o code_name or just "run code" with Vs Code's Code Runner. Both will give me the error but running the code with ./code_name works fine, the functions are applied. I can ignore the error message and still run the code. If you use Replit, it works as well, without any messages.
I use VS Code and run my code in two different ways. Either Code-Runner or the Terminal, usually Code-Runner and Terminal when it doesn't work with it.
When running the following code:
#include <stdio.h>
// #include <math.h>
int main(){
printf("%f\n", pow(2,3));
return 0;
}This happens with Code-Runner:
>https://imgur.com/a/YsgSyvq (First Image)
Note that Code-Runner automatically creates the .exe and I can run the code with the terminal (PowerShell) by using
./code_name
>https://imgur.com/a/YsgSyvq (Second Image)
But again, when I try to use
gcc Working_Numbers.c -o WN
to build the code, it sends a warning message, telling me that I must use math.h or declare pow() (the math function).
But I can still do
./WN
And the code runs without issues.
>https://imgur.com/a/YsgSyvq (Third Image)
So does C already have these math functions built into it or is #include <math.h> necessary?
-lm needs to added to the command line after the file that requires that library for example if main.c required the math library then you would use:
gcc -x c main.c -lm
You can see a live example here, there are three command lines available in the example. One without -lm, one with -lm before the file that needs it one after the files that needs it.
For completeness sake if we refer to the gcc docs on options for Linking it says the following for -l:
[...]It makes a difference where in the command you write this option; the linker searches and processes libraries and object files in the order they are specified. Thus, ‘foo.o -lz bar.o’ searches library ‘z’ after file foo.o but before bar.o. If bar.o refers to functions in ‘z’, those functions may not be loaded. [...]
You need to link the math library. Use the -lm option on the command line.
The functions in stdlib.h and stdio.h have implementations in libc.so (or libc.a for static linking), which is linked into your executable by default (as if -lc were specified). GCC can be instructed to avoid this automatic link with the -nostdlib or -nodefaultlibs options.
The math functions in math.h have implementations in libm.so (or libm.a for static linking), and libm is not linked in by default. There are historical reasons for this libm/libc split, none of them very convincing.
Interestingly, the C++ runtime libstdc++ requires libm, so if you compile a C++ program with GCC (g++), you will automatically get libm linked in.
Remember that C is an old language and that FPUs are a relatively recent phenomenon. I first saw C on 8-bit processors where it was a lot of work to do even 32-bit integer arithmetic. Many of these implementations didn't even have a floating point math library available!
Even on the first 68000 machines (Mac, Atari ST, Amiga), floating point coprocessors were often expensive add-ons.
To do all that floating point math, you needed a pretty sizable library. And the math was going to be slow. So you rarely used floats. You tried to do everything with integers or scaled integers. When you had to include math.h, you gritted your teeth. Often, you'd write your own approximations and lookup tables to avoid it.
Trade-offs existed for a long time. Sometimes there were competing math packages called "fastmath" or such. What's the best solution for math? Really accurate but slow stuff? Inaccurate but fast? Big tables for trig functions? It wasn't until coprocessors were guaranteed to be in the computer that most implementations became obvious. I imagine that there's some programmer out there somewhere right now, working on an embedded chip, trying to decide whether to bring in the math library to handle some math problem.
That's why math wasn't standard. Many or maybe most programs didn't use a single float. If FPUs had always been around and floats and doubles were always cheap to operate on, no doubt there would have been a "stdmath".
I need to run math functions from a text file but I dont know how to do this efficiently. At the moment I am just comparing the string input to case statements but it quickly gets out of hand with the amount needed. Does anyone know how to import math functions from a text file and run them? For example x*sin (x)/cos (x).
There's no "execute this as if it were code" in C because C is a compiled language- there's nothing that understands C code at run time. You need to write a parser to split each equation up into parts and then write code to handle each math operation.
I'd use a ready-made library like this one: http://www.gnu.org/software/libmatheval/
If you want to do it yourself, it's not impossible, but it's not too easy to write a reasonably bug-free library for it. Generally, you can parse the text to build up a tree (at least conceptually), in which the leaves are your variables and the other nodes are functions. For x*sin(x)/cos(x), it would be something like this (although, I think I might have gotten the multiplication and division reversed, not that it matters):
*
--x
--/
--sin
--x
--cos
--xAfterwards, you can parse this tree, e.g. in post-order to have something equivalent to an RPN calculator. I really don't recommend this for anything more than an academic exercise.
EDIT: It also occurs to me that you could use a scripting language which you can run from within C, like Lua. If you run their example and type in something like "print(math.cos(math.pi)/2)" or "a=1 b=2 print(a+b)", it'll give you an answer back. It might be overkill for what you're doing.