This is an extremely weird question, but I am still curious. I have a source code a.c, in it, I have some magic code that compiles a different code b.c in the same directory. Hence, during runtime, b.c is compiled and perhaps ran.
I apologize for this question to be vague, but is this something that's been done before? If not, is there any way to do so?
a.c:
#include <stdio.h>
int main() {
puts("a: compiling b.c");
system("gcc -o b b.c");
puts("a: executing b");
system("./b");
puts("a: done");
return 0;
}
b.c:
#include <stdio.h>
int main() {
puts("b: hello world");
return 0;
}
output:
a: compiling b.c
a: executing b
b: hello world
a: done
Yes, you can fork and exec to run the compiler, and then fork and exec again to run the compiled code. The other option is to use the system function to run the compiler, and then call system again to run the compiled code.
Related
I am new to C language but I use Gitpod for other languages. I would like to know how to run this simple "hello world" main.c program from the Gitpod interface step by step?
#include <studio.h>
void main(){
printf("hello")
}
Many thanks !
After fixing the errors you can compile the code with gcc main.c and run the binary a.out.
Errors as already mentioned:
studio.h -> stdio.h
...hello") -> ...hello");
after the printf("hello")
you should put ;
//like this
printf("hello");
#include <stdio.h>
int main(){
printf("hello");
return 0;
}
I am writing a program using execv() that compiles and runs another program. I've written up a simple C program named helloWorld.c that when executed outputs, "Hello world," and a second file named testExec.c that is supposed to compile and run helloWorld.c. I've been looking around everywhere to find a way to do this, but I haven't found any answers. The code in testExec.c is:
#include <stdio.h>
#include <unistd.h>
int main(){
char *args[] = {"./hellWorld.c", "./a.out", NULL};
execv("usr/bin/cc", args);
return 0;
}
testExec.c compiles with no errors. However, when I run it I get an error that says, "fatal error: -fuse-linker-plugin, but liblto_plugin.so not found. compilation terminated." Which I think means helloWorld.c is being compiled but when it comes time to run helloWorld.c this error is thrown. I thought maybe that was because I had a.out and helloWorld.c prefaced with './'. I removed './' from both, then either one individually, and still no luck.
I also did 'sudo apt-get install build-essential' along with 'sudo apt-get install gcc'. I wasn't sure if that would resolve the issue but I really wasn't sure what else to try. Anyway, any help would be appreciated!
You're missing the leading slash when calling cc.
Also, the first argument in the argument list is the name of the executable. The actual arguments come after that. You're also not using -o to specify the name of the output file.
#include <stdio.h>
#include <unistd.h>
int main(){
char *args[] = {"cc", "-o", "./a.out", "./hellWorld.c", NULL};
execv("/usr/bin/cc", args);
return 0;
}
EDIT:
The above only compiles. If you want to compile and run, you can do this:
#include <stdio.h>
#include <unistd.h>
int main(){
system("cc -o ./a.out ./hellWorld.c");
execl("./a.out", "a.out", NULL);
return 0;
}
Although this is probably best done as a shell script:
#!/bin/sh
cc -o ./a.out ./hellWorld.c
./a.out
I was wondering how this works, creating a library and preloading it so a program can use it instead of the one in the include statement.
here is what I am doing and is not working so far .
//shared.cpp
int rand(){
return 33;
}
//prograndom.cpp
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int main(){
srand(time(NULL));
int i = 10;
while(i--) printf("%d\n", rand()%100);
return 0;
}
Then in the terminal:
$ gcc -shared -fPIC shared.cpp -o libshared.so
$ gcc prograndom.cpp -o prograndom
$ export LD_PRELOAD=/home/bob/desarrollo/libshared.so
and finally
$ LD_PRELOAD=/home/bob/desarrollo/libshared.so ./prograndom
which doesnt print 33, just random numbers...
Your programs are C programs, but the cpp file extension implies C++, and GCC will interpret it that way.
That's an issue because it means that your function rand (in shared.cpp) will be compiled as a C++ function, with its name mangled to include its type-signature. However, in main you #include <stdlib.h>, which has the effect of declaring:
extern "C" int rand();
and that is the rand that the linker will look for. So your PRELOAD will have no effect.
If you change the name of the file from shared.cpp to shared.c, then it will work as expected.
Other alternatives, of dubious value, are:
Declare rand to be extern "C" in your shared.cpp file. You can then compile it as C++.
Force compilation as C by using the GCC option -x c.
I'm trying to cross compile net-snmp for mips64, and in order to do that I need the libperl library. I tried to configure libperl for mips64 using the following command:
./Configure -Dcc=/home/toby/x-tools/mips64-n64-linux-gnu/bin/mips64-n64-linux-gnu-gcc -Dprefix=/home/toby/perl
But I got the following error:
Checking your choice of C compiler and flags for coherency...
I've tried to compile and run the following simple program:
#include <stdio.h>
int main() { printf("Ok\n"); return(0); }
I used the command:
/home/toby/x-tools/mips64-n64-linux-gnu/bin/mips64-n64-linux-gnu-gcc -o try -O -I/usr/local/include try.c
./try
and I got the following output:
./try: 1: Syntax error: "(" unexpected
The program compiled OK, but exited with status 2.
(The supplied flags or libraries might be incorrect.)
You have a problem. Shall I abort Configure [y]
How can I fix this?
I'd turn:
#include <stdio.h>
int main() { printf("Ok\n"); return(0); }
Into:
#include <stdio.h>
int main() {
printf("Ok\n");
return(0);
}
And then run the compile command by hand to see which line really contains the syntax error.
That looks like an error from your shell and not the compiler. Particularly because gcc doesn't return "status 2" for a syntax error, but bash does. The problem happens because you have cross compiled a program called ./try for mips64. How do you expect ./Configure to execute it on your host pc? – indiv
I wrote little program to print "Hello world" in C. I'm not a C programmer, but I liked to try it. In my program there is an error. Please tell me what is it?
This is my program:
int main(){
printf("Hello World");
}
I wrote this with my Java Experiences. I can't find what is wrong.
You can't directly use printf() function as in Java. You should tell the compiler that you are going to use the input/output stream. You can tell it in this line:
#include <stdio.h>
and also you should enter this line at the end of the source code:
return 0;
this will tell the compiler :
"If the program succeed It will return 0 otherwise It will return any other number"
This means if your program is successful main() function will return 0. Then the compile know the program is Ok.
Then at last your complete code is:
#include <stdio.h>
int main() {
printf("Hello world");
return 0;
}
To compile this and see the word "Hello World", just save this file as a .c file and Open cmd in your program directory and type
gcc hello.c -o hello && hello
(Replace the 'hello.c' with your filename, and 'hello' with the name you want to put with your .exe file)
Remember My computer is Windows. And this compile code is for windows. If your OS is UNIX like OS. then use this code to compile:
gcc hello.c -o hello
./hello
A full hello world program in C:
#include <stdio.h>
int main(void) {
printf("Hello World\n");
return 0;
}
Then compile (assuming gcc) and execute it:
gcc -o test test.c
./test
First, you have to use a header file.
#include <stdio.h>
What that does is bring up a header file with a bunch of commands in them. That will make it recognize the "printf" piece of code.
Next, you have to close your program. By not having a closing statement, the program will not compile because it doesn't know if that is the end of the code. Use this at the end of your program...
return 0;
That closes the program, meaning that the compiler can stop looking for other code. You may also want to look at some programming manuals (there are dozens of free online ones) to learn about the syntax.
One last thing: Most pieces of C code require a semicolon at the end. This is not true for the "int main" statement, nor is it for the header file which I have defined above. The "return" function that closes the program, does however, need a semicolon.
Hoped this helped.
Should also include a pause at the end:
#include <stdio.h>
int main(void) {
printf("Hello World\n");
//Read a character from the console
getchar();
return 0;
}
Just like import in Java programs, in here you have to include libraries you're using in your program. You have used library function printf, but not included stdio.h.
I agree there are many ways to write one of the simplest way is
#include<stdio.h>
int main(void){
printf("Hello World\n");
return 0;
}
You can even use different ways as suggested above.
You should first look at the structure of "main". Try to understand the various parts as already explained so well in the above answers.
"#include" : The preprocessing directives to be included in the program. But why? Because you are trying to use the functions defined inside them.
int : The return type of "main" program. But why? Because the function calling "main" needs to know if the "main" program has functioned correctly.
main : The entry point of your code. Dont ask why here :-)
main( void ) : To tell the compiler that we are not passing any arguments to program "main"
return 0 : Beacuse you promised "main" that you will return something if "main" will function properly.
Finally the code:
#include <stdio.h>
int main( void )
{
printf( "Hello World\n" ) ; //Notice the '\n' here. Good coding practice.
return 0 ;
}
#include <stdio.h> //Pre-processor commands<br/>
void main() //Starting point of the program<br/>{ //Opening Braces
printf("Hello World\n"); //Print Hello World on the screen<br/>
return 0;
} //Ending Braces
Check it once it will work, I have written it with comments:
#include<stdio.h> //Pre-processor commands
void main() {
printf("Hello World\n"); //Print Hello World on the screen
}
A full hello world program in C:
#include <stdio.h>
int main(void) {
printf("Hello World\n");
return 0;
}
Then compile (assuming gcc) and execute it:
gcc -o test test.c
./test
You can't use printf() function as in Java. You have to tell the compiler what you are going to use.
You can tell this as follows:-
#include <stdio.h>
You must enter this line in last:-
return 0;
Then Your complete code is:-
#include <stdio.h>
int main(){
printf("Hello World");
return 0;
}
For compiling this and see the word "Hello World", just save this file as a .c file and Open cmd in your program directory and type:-
gcc hello.c -o hello && hello
(Replace the 'hello.c' with your filename, and 'hello' with the name you want to put with your .exe file)
Remember My computer is Windows. So I can compile only for Windows OS.
#include <stdio.h>
int main() {
// printf, used to print (display) Hello World
printf("Hello World ! ");
// return 0, as the main function is of type int so it must return an integer value
return 0;
}