I wanted to compile the below code in VS Code, but I'm fetching this error using "code runner". I've looked up everywhere, but it didn't solve my issue.
I want to implement this T(n) = 2T(n/2) + nlog(n)
q2.c
// b. T(n) = 2T(n/2) + nlog(n)
#include <stdio.h>
#include <math.h>
int func(double n)
{
return (2*func(n/2) + n*(log(n)));
}
int main()
{
double n, result;
printf("Enter the value of 'n' \n");
scanf("%lf",&n);
printf("Hey");
result = func(n);
printf("%lf \n",result);
printf("Hey");
return 0;
}
Console:
user#user-H310M-DS2:~/Desktop/C programming/Assignments$ cd "/home/user/Desktop/C programming/Assignments/" && gcc q2.c -o q2 && "/home/user/Desktop/C programming/Assignments/"q2
/tmp/ccnNXN3L.o: In function `func':
q2.c:(.text+0x3a): undefined reference to `log'
collect2: error: ld returned 1 exit status
Visual studio code has nothing to do with your issue, you are not compiling with it. Because it is an IDE (or source code editor), not a compiler. I guess you are using it on some Linux or POSIX system. BTW my preferred source code editor is GNU emacs. So your IDE is running some compilation commands (and you need to understand which ones and what these commands are doing). You could run these commands in a terminal (and that actually might be simpler).
As your console logs shows, you are compiling with GCC. Some gcc command has been started (by Visual studio code probably).
Read carefully about Invoking GCC. Order of arguments matters a lot!
You should compile your code with
gcc -Wall -Wextra -g q2.c -lm -o q2
Let me explain this a bit:
gcc is your compiler front-end (the actual compiler is cc1 but you never use it directly; you ask gcc to run it)
-Wall asks for almost all warnings
-Wextra asks for extra warnings. You'll be happy to get them
-g asks for debugging information in DWARF. You really want to be able to use the gdb debugger, and gdb practically needs debugging information.
q2.c is the source file of your sole translation unit
-lm is for your math library. You are using log(3) and its documentation mention that.
-o q2 tells gcc to put the executable in q2 (the actual work is done by the ld linker invoked by gcc)
How to configure visual studio code to use that command is your business. You could otherwise type the above command in a terminal. Then you can run your q2 program by typing ./q2 in a terminal for your shell (and you could use gdb on it).
Notice that gcc is starting other programs (like cc1, as, ld). If you want to understand which ones, insert -v after gcc in the command above.
Be sure to read the documentation of every function you are using (so read printf(3), scanf(3), log(3) at least...) and of every program you are using (e.g. of gcc and of Visual studio code).
Once you'll write bigger programs made of several translation units (e.g. foo.c, bar.c, gee.c), you would want to use some build automation tool (because compiling all of them every time with gcc -Wall -Wextra -g foo.c bar.c gee.c -lm -o qqq is possible, but inconvenient). You could learn to use GNU make (or ninja).
Read How to debug small programs. Don't expect your program to work as you want at first.
BTW, study the source code of some existing free software programs (but start with simple projects, e.g. on github, of less than a hundred thousand lines). This could teach you many useful things.
I'm not sure how VSCode compiles programs, but since it uses GCC, it's likely that you need to link the math library libm when compiling, by supplying an argument -lm to GCC.
Just a tweak to code runner's settings.json under file->preferences->settings of VS Code :
I've added the below line
"code-runner.executorMap":
{
"c": "cd $dir && gcc -Wall -Wextra -g $fileName -lm -o $fileNameWithoutExt && $dir$fileNameWithoutExt",
}
It's working now.
Related
I am doing the CS50 class, I have installed the cs50.h.
Based on the instructions I used the following command in terminal to compile my simple program and just want to make sure I understand everything im asking terminal to do.
Line is:
gcc -g hello.c -o hello -lcs50 -lm
I know the following*: gcc =
gcc = gnu compiler for C
-g = generate source-level debug information
Hello.c = name of the file we want to compile
-o = write output file
hello = our output file name
Can anyone tell me what -lcs50 and -lm are? My guess is that its calling on the library lcs50 in (-lcs50) but again this is a guess and would like to know for sure.
Everything works as it should with no issues
Thanks,
Mostly correct.
-o is not required to generate the output file, it's only needed to customize the name. (-o and the following name can only appear together).
-lcs50 means "link the library called cs50", not lcs50. It will try to find this file using several different name patterns, e.g. libcs50.so (on Linux), [lib]cs50.dll[.a] (on Windows), libcs50.a (on both), something else on Mac.
-lm links the standard math library, but I don't think you need to manually specify it on most modern GCC distributions.
Yes. For -lm, it's for the maths library, which is not linked by default. This is explained well at Why do you need an explicit `-lm` compiler option.
Is there a way to see what the expanded code will look like after preprocessing?
Found many answers to my question online but all of them used a lot of terms which were completely alien to me.
Seeing expanded C macros
Determine the expansion of a C macro
I am a complete beginner in programming. Learning C from 'Let us C' by Y.K. Currently in the 12th chapter
'C Preprocessor'.
Can someone explain this in simple terms or should I just leave it for now and get back to it later?
using Code:Blocks as the IDE and gcc as the compiler.
Edit:-
#include<stdio.h>
#define AREA(x) (3.14*x*x)
int main()
{
int r1=1,r2=2;
float ar1,ar2;
ar1=AREA (r1);
printf(" %f",ar1);
ar2=AREA (r2);
printf(" %f",ar2);
printf(" %f",ar1/ar2);
printf(" %f",AREA (r1)/AREA (r2));
}
Compile your code from the terminal, with the -E flag: gcc my_code.c -E.
This will print the preprocessed code directly to the terminal. If you want to save it to a file instead, add something like -o result.txt at the end.
Read the documentation of the GCC compiler.
Read also some C reference website.
There is a chapter about Invoking GCC. Spend an hour to read it.
You also want to read the documentation of the CPP preprocessor, and probably of GNU binutils.
You could compile your C file ems.c using gcc -Wall -Wextra -g -H ems.c -o ems-prog. Once you have no warnings, use the GDB debugger to understand the behavior of your executable ems-prog
You could run gcc -Wall -Wextra -g -C -E ems.c -o ems.i to obtain, inside the ems.i file, the preprocessed form of ems.c
You can run compilation commands in some terminal emulator.
Later, you want to use GNU make (or ninja) or some other build automation tool to drive compilation commands. Of course, you need to read their documentation.
Study for inspiration the source code of existing free software coded in C, for example GNU bash.
I want to be able to pass arguments to GCC from my C source code, something like this...
// pass the "-ggdb" argument to GCC (I know this won't work!)
#define GCC_DEBUG_ARG -ggdb
int main(void) {
return 0;
}
With this code I'd like to simply run gcc myfile.c which would really run gcc myfile.c -ggdb (as the "-ggdb" argument has been picked up from the C source code).
I'm not interested in using make with the CFLAGS environment variable, I just want to know if its possible to embed GCC options within C source code
What you want to do is not possible in general.
However, recent GCC (e.g. GCC 8 in end of 2018) accepts many options and some of them could be passed by function attributes or by function specific pragmas (However, they don't accept -g but do accept -O2).
Also, you can use -g in every compilation (with GCC, it is mixable with optimization flags such as -O2; so runtime performance won't suffer. Of course the -g will increase compile time and size of produced object file). Notice that (on Linux) the DWARF debug information is visible in the generated assembler file (e.g. try to compile your foo.c with gcc -Wall -g -O -S -fverbose-asm foo.c, look into the generated foo.s, and repeat by removing the -g)
I'd like to simply run gcc myfile.c
That is a very bad habit. You should run gcc -Wall -Wextra -g myfile.c -o myprog to get all warnings (you really want them) and debug info in your executable myprog. Read How to debug small programs before continuing coding your program.
I'm not interested in using make with the CFLAGS environment variable
But you really should. Using make or some other build automation tool (e.g. ninja, omake, rake, etc, etc....) is, in practice, the conventional and usual way of using GCC.
Alternatively, on Linux, write a tiny shell script doing the compilation (this is particularly worthwhile if your program is a single source file; for anything bigger, you really should use some build automation tool). At last, if you use emacs as your source code editor, you could add a few lines of comments (like at end of my manydl.c example) specifying Emacs file variables to tune the compilation (done from emacs)
If these conventions surprise you, read about the Unix philosophy then study -for inspiration- the source code of some existing free software (e.g. on github, gitlab, or in your favorite Linux distribution).
At last, GCC itself is a free software project (but a huge one of more than five millions lines of mostly C++ source code). So you can improve it the way you desire (if you follow its GPLv3+ license), after having studying somehow its source code. That would take you several months (or years) of work (because GCC is very complex to understand).
See also this answer to a related question.
You might also (but I recommend not to, because it is very confusing) play tricks with your PATH variable and have some directory there -e.g. $HOME/bin/, ahead of /usr/bin/ which contains /usr/bin/gcc, with your shell script named gcc; but don't do that, you'll be confused. Instead write some "generic" mygcc shell script which would run /usr/bin/gcc and add appropriate flags to it (I believe it is not worth the effort).
I am using Linux now, and trying to compile this by gcc BUT.......
this is my truly simple code:
#include <stdio.h>
int main(){
printf("Hello world\n");
return 0;
}
and this is so much weird output:
./try.c: line 3: syntax error near unexpected token `('
./try.c: line 3: `int main(){'
why is it?
I have tried the right way to compile it, such:
gcc file_name.c -o file_name and other types of way of compiling
chmod +rwx file_name.c
./file_name.c
but still I got that result, why?
You have to compile the code first.
Follow these steps.
gcc try.c -o try.out
to compile the code. The -o option is given to give a custom name to the executable that will be produced.
Then, you can run it by typing
./try.out
To run the executable.
Be informed though, that there are a number of command line options that you can use to get the information about your code and add more functionality. See this page for more information.
You are trying to execute the .c file, remove the trailing .c from the name of the file you want to execute.
Like this:
gcc -Wall -Wextra -pedantic -Werror -o executable file_name.c
You should not need to make it executable, it should already be executable since the compiler will do that.
./executable
As you see, I've passed some parameters to gcc to let it help in diagnosing problems, sometimes these problems are caused by your lack of knowledge and some other times because you write code quickly and miss some details. So using them is good (although compilation is slower, but that doesn't matter if you have a good and fast machine, wehreas having issues in the code does matter).
The meaning of these flags are as follows
-Wall Enable all warnings. Really some are not enabled, but most are.
-Wextra Enable extra warnings.
-pedantic make the compiler pedantic, i.e. stick strictly to the desired (default for this version of gcc) standard.
-Werror Consider that warnings are errors.
Also, you could have guessed this if you see what the error says
./try.c: line 3: syntax error near unexpected token `('
./try.c: line 3: `int main(){'
as you can see the shell is trying to execute the source code as if it was a shell script, so you can immediately notice that this is not the executable file generated by gcc, and then you would notice the .c in the file name.
Try
gcc try.c
./a.out
Compiles the code and runs it. Please read the manual page for gcc and there are many delights to behold (extra checking etc)
On this beginner tutorial at TutorialsPoint, it says to save the code as test.c and compile it using "$gcc test.c -o demo" command at CMD.
But I don't have $gcc. What is it?
Let's split this into parts:
$ is a character indicating that the shell is ready to receive a command. It is not part of the command.
gcc is an executable executing the GNU C compiler from the GCC toolchain.
test.c -o demo are arguments supplied to gcc.
The GCC toolchain is only available natively for GNU systems such as Linux. Using MinGW or CygWin you can ape its functionality, though.
Notes:
A nice comment, which I second, to your question by #iharob:
Don't use gcc test.c -o demo specially if you are a beginner, use gcc -Wall -Wextra -Werror test.c -o demo.
The additional switches make the compiler point out more warnings.
GCC (GNU Compiler Collection. Upper case.) is a set of compilers, that can compile several languages.
gcc (lower case) is a command that compile the code you wrote, using the C compiler that GCC includes, into a working C program. Similar commands are g++ for C++ code, gcj for Java code, etc.
Note GCC is intended for Linux or other Unix-like systems (You can use it in Mac OS X with the help of xcode). If you are using Windows, consider [MinGW] (http://www.mingw.org/) or CygWin https://www.cygwin.com/.
As a beginner, if you still have trouble, consider use Dev-C++, an IDE (integrated development environment) that compiles C and C++. It does all the compiler things for you.