(I am running Linux Ubuntu 9.10, so the extension for an executable is executablefile.out) I am just getting into modular programming (programming with multiple files) in C and I want to know how to compile multiple files in a single makefile. For example, what would be the makefile to compile these files: main.c, dbAdapter.c, dbAdapter.h? (By the way, If you haven't figured it out yet, the main function is in main.c) Also could someone post a link to the documentation of a makefile?
The links posted are all good. For you particular case you can try this. Essentially all Makefiles follow this pattern. Everything else is shortcuts and macros.
program: main.o dbAdapter.o
gcc -o program main.o dbAdapter.o
main.o: main.c dbAdapter.h
gcc -c main.c
dbAdapter.o dbAdapter.c dbAdapter.h
gcc -c dbAdapter.c
The key thing here is that the Makefile looks at rules sequentially and builds as certain items are needed.
It will first look at program and see that to build program, it needs something called main.o and dbAdapter.o.
It will then find main.o. However, to build main.o, it will need main.c and dbAdapter.h (I assume dbAdapter.h is included in main.c).
It will use those sources to build main.o by compiling it using gcc. The -c indicates the we only want to compile.
It does the same thing with dbAdapter.o. When it has those two object files, it is ready to link them. It uses the gcc compiler for this step as well. The -o indicates that we are creating a file called program.
GNU make should be what you're looking for.
Related
I have two C files, program.c and tests.c, that each contain a main function.
program.c is a standalone program, that compiles and run normally on its own. But I would like to also be able to use some of its functions in tests.c (without using a common header file). Is there a way of doing this?
If I insert the prototype of the function I want from program.c into tests.c and compile with:
gcc -o program.o -c program.c
gcc -o tests.o -c tests.c
gcc -o tests tests.o program.o
I obtain an error duplicate symbol _main, which I understand since there are indeed two `main' functions.
I basically would like to be able to treat program.c both as a standalone program and as a library, similarly to what could be done in Python with if __name__ == '__main__'.
If you need to have two separate distinct executables for which some of the functionality between them is similar you can share the common functionality by placing relevant functions into a third file, and compiling as a portable executable, DLL in Windows. (or shared library in Linux.) Each of these file types contain sharable, executable code, ithout the main() function, designed to be linked during compile time, and dynamically loaded into your executable at runtime.
Here is a step by step set of instructions for shared library using GCC and Linux.
Here is a step by step example for creating DLL using GCC in windows.
So I managed to achieve what I wanted thanks to the comment from #pmg:
I compile program.c into a standalone binary (gcc -o program program.c), but I also compile it into an object file with "main" renamed (gcc -c -Dmain=mainp -o program.o program.c).
I can then use this object file (that does not contain a "main" symbol anymore) to compile tests.c: gcc -o tests tests.c program.o.
Thanks #pmg, I did not know this use of the -D option.
I have written c program, Which has 3 file(.c ) , Main program has
two threads and one file has mysql connection function, One file has
thread functions definition. I don't know how to compile all these
codes, Normally I tried like this,
cc -pthread main.c
But if I compile like this I am getting error called mysql functions
are undefined But I have written thread as separate program and
mysql as separate program and complied individually , it complied
successfully and I got output. So please help me to compile my
project File names are,
main.c (2 threads are declared) functions.c (thread function
definition, and mysql func declared) db.c ( mysql function
definition)
please help to compile my code?
You have two basic options when compiling multiple .c files:
Option 1)
cc file1.c file2.c file3.c -o executable_name
Advantage: simple
Disadvantage: if all you change is one file you are recompiling all the files
Option 2)
cc file1.c -c -o file1.o
cc file2.c -c -o file2.o
cc file3.c -c -o file3.o
cc file1.o file2.o file3.o -o executable_name
Advantage: If you change one file you do not have to recompile everything
Disadvantage: Multiple commands (but you should use a Makefile at this point)
The -c flag tells the compiler to compiler but not link. You don't want to link as you have not compiled all of your files. The final invocation of cc links all the .o files into the executable executable_name
It is a little bit difficult to understand exactly what you need, but I can tell you from what you've stated that you'll need to include specific libraries in your compile statement you currently are not. Also, a -l flag needs to prefix your libraries.
Try something like this:
gcc -lpthread main.c functions.c db.c -o main $(mysql_config --libs)
To explain, mysql_config --libs returns all the configuration libraries needed to run mysql ddl inside your C program.
Given your updates on your file declarations I'm guessing you're a Java programmer. C is not Java. If you are declaring functions you are only going to use once in main.c you should put them inside main.c unless you need them to be portable.
I have three C files in total. One is a header [.h] file, two are source [.c] files.
The .h file is called encryption.h and the corresponding source file is encryption.c. The encryption.c has logic, but no main() function. My second c file is called main.c. There I have the main() function that calls methods from encryption.c.
I am compiling these files within terminal on Mac OSx. I am confused on how to compile this, I have tried the following:
gcc -c main.c
gcc -c encryption.c
gcc -c encryption.h
gcc main.o encryption.o encryption.g.gch -o encrypt
This doesn't seem to work though, it says I have a precompiled-header already. I tried finding the answer online, I know it has to be simple, but I haven't had much luck. What is the issue here?
Don't compile the header file. Header files are meant to be included to the source files (using #include directive, in c). Just compile the source files and link them together. Something like
gcc -c main.c
gcc -c encryption.c
gcc main.o encryption.o -o encrypt
or, for shorthand,
gcc main.c encryption.c -o encrypt
Note: If you're bothered about the presence (or absence) of header files while compilation, check the pre-processed output of each source files using gcc -E option.
I am just starting out with C and now I am at the part where I want to learn about Makefiles. I am starting out small but already failing ;)
I have a very simple Makefile which just compiles the main.c to a main.o and then to an executable. But I get an error saying I have a syntax error. I use g++.
The command that i use are:
g++ make Makefile << name of the make file
And the Makefile is set up like this:
main.o: main.c main.h
[TAB] g++ -c main.c
main: main.o
[TAB] g++ main.o -o main
To run make on the Makefile (the default name), invoke the make command:
$ make
Don't try to call g++ with the makefile, the compiler knows nothing about makefiles.
EDIT: You say you don't have the make command, in a comment. Then you need to get it. :) There are several versions of make for Windows, here is GNU make (which is common in Linux and other Unix-like environments) ported to Windows.
I'm trying to compile a program that have main.c and a lot of .c and .h files .
Is there any way to compile and link without passing all .c file in the gcc command
like
gcc main.c file.c file2.c -o main
Your shell can expand wildcards. So you can:
gcc *.c -o main
Of course, you'll have to make sure that you don't have any extra *.c files in the directory that you don't actually want compiled. A better option is to use a build system such as Make or SCons.
'make' is the tool for building C apps. Below is the hello world version.
$ cat main.c
#include <stdio.h>
int main (char *argv[], int argc) {
printf("Hello World\n");
return 0;
}
$ make main
cc main.c -o main
$ ./main
Hello World
Edited in deference to Shahbaz comment:
The original question was trying to simplify the command-line for gcc. The right direction for the programmer is to learn about make. Since there is a bit of a learning curve with make, I wanted to offer simple stepping stone which does something useful. By getting started in this way, you don't need a make file. Simply type 'make programname' as shown above. Make uses its default rules and associated varabiles. $(CC) -c $(CFLAGS) $(CPPFLAGS) The astute programmer can build on this by setting well-know variables.
From here one can tinker with a makefile. In the spirit of stepping stones, consider this trival makefile
$ cat makefile
SRCS = main.c
OBJ = ${SRCS:.c=.o}
CC=gcc
main: ${OBJ}
$ make
gcc main.o -o main
By setting the well-known make variable CC to control which compiler is used. OBJ is computed from the list of source files. The trival target starts one on the road to rules.
Anyway, my hope is this post and other answers get the original questioner on there way.
Regards,
-jk
If you're asking about the command-line, you can just use wildcards to specify all the .c files as #Man of One Way suggested. But in general, C applications of any-but-trivial-size are built using "makefiles" which are extremely helpful.
You might want to read a tutorial such as http://www.cs.umd.edu/class/fall2002/cmsc214/Tutorial/makefile.html
gcc -o main -I. `find . -name "*\.c"`
This way you could have the .c and .h files in subfolders if you wish.
However, this is not a good way of doing it. A better way would be to create a Makefile
As already said, make is the best way to go
Learn just what you need at every point
Besides, it is important to also use some flags that will help you out while coding:
-Wall -> sets all warning flags
-g, -ggdb -> generates debug code
-ansi, -std=c99
A really good book on how to use make is,
http://shop.oreilly.com/product/9780937175903.do