I wrote this in notepad and then compiled it with lcc-win, using the command lc hello.c
#include <stdio.h>
int main(void)
{
printf("Hello World\n");
return 0;
}
The resulting exe was 100 KB. Seems kind of huge for a program that just prints Hello World. Is this normal? Can I reduce the size? 100 KB isn't really an issue these days but it still seems kind of big for what it does. Wouldn't be too bad if every C code I write comes out as a 100 KB exe though.
1- Everytime you use the include <> tag you do make a link with a c library and load it in your programm.
That is also why it is important to include only in the files that actualy need the library functions.
2- On the other part, the binary that you generate is always full of important informations (cf : libelf or ASM), headers, steps that needs to be here if you want to programm to be run nicely. This does take space to.
This is a really simple question, what happens to the lcc-win is the same with the C Compiler Digital Mars, he do not link the exe with dlls containing the functions printf and etc., functions are linked together with EXE, so no requerindo that your computer has the DLLs.
Look, I created a simple Hello World EXE, and I opened hin in Hex Editor.... the printf function is stored in msvcrt.dll, and, the exe don't have this dll in import section...
And, u can found the source definition in this other picture:
Use this style of function definition is more fast then make a dll call....
Related
I'm new to programming and currently I'm learning C programming. I'm writing codes on the code blocks and in it using GCC compiler. When I create a new project, (as you know it creates main.c file with it) and due to that I'm not able to compile another file in that project.
File 1:
#include<stdio.h>
int main()
{
int a,b,c,d;
printf("Enter three numbers\n");
scanf("%d%d%d",&a,&b,&c);
d=a;
if(b>d)
d=b;
if(c>d)
d=c;
printf("\n The maximum of three numbers is %d",d);
}
File 2: main.c
#include <stdio.h>
int main()
{
printf("Hello world!\n");
return 0;
}
When I compile the first programme, it shows the following error:
multiple definition of 'main'
first defined here
I've searched every where I could and I'm not able to solve this. In one of the answers here on stack overflow, someone had suggested to write this in
(Project->Build options...->Linker settings (tab))
-Wl,--allow-multiple-definition
When I wrote it, there were no errors. But it wasn't able to run my File 1 and instead, it runs that main.c file. Even when I close the main.c file, it opens there again and runs main.c file which gives the output "Hello World!".
Initially when I was using code blocks there were no such errors. I don't know why this is happening and I've not much knowledge about compilers.
As noted in comments you can only have one main function.
So when you start a new project you need to replace the main.c file with the main.c file you want to use. Or you can edit the 'hello world' main.c program.
When you start a new project in code::blocks you can get a new directory with a simple program that prints 'Hello World'. This file is usually main.c. You need to edit this file or replace it. The reason that code::blocks puts this simple main.c program in the new project is so that you can compile it and test your system without having to write a new program.
Some computer languages allow you to use the same function name for different functions ( which are identified by their parameters and sometimes return types ). That's called overloading. C does not allow this. Functions in C must have unique names.
The main() function is a special one in C as it is used as the standard entry point for applications. That is, the main() function will be called first and your application should start and (typically) end in that function.
As a beginner I would suggest you avoid automated editor features that create and build projects for you. You will miss out on learning how things work doing that. Use an editor to start from empty files and learn how they all connect and how to use the compiler from the command line. The command line is something every beginner should start from, IMO.
It may be harder to learn, but it will give you a much better feel for what is going on.
I guess what you maybe trying to do is have multiple sandbox "gists" that you may wanna run all as their own main function. If that is the case, then just close your project and open the files directly. As long as they are not in a project, they will run fine.
I'm trying to use YCM for the first time so in order to make it work I decided to give a chance for the YCM-Generator, which generates the .ycm_extra_conf.py file automatically based on the makefile.
So far my program is just a simple hello world.
#include <stdio.h>
int main()
{
printf("Hello World!");
return 0;
}
I'm using the CMakeLists.txt trick to generate the makefile.
file(GLOB sources *.h *.c)
add_executable(Foo ${sources})
then after executing the YCM-Generator script, I get this output
Running cmake in '/tmp/tmp_YknVy'... $ cmake
/home/pedro/Desktop/Projetos/teste
Running make... $ make -i -j4
Cleaning up...
Build completed in 1.5 sec
Collected 2 relevant entries for C compilation (0 discarded).
Collected 0 relevant entries for C++ compilation (0 discarded).
Created YCM config file with 0 C flags
YCM plugin does find the .ycm_extra_conf.py file, but the auto-completion doesn't work right, for example, if I type "floa", it doesn't suggests "float", but It only suggests things that I used before like "int" or "printf".
Am I missing something or this is working as intended?
So I fixed it.
For c it does require a .ycm_extra_conf.py , while a friend of mine could make it work without one in c++.
The auto complete only suggest automatically functions that were previously used, if you don't remember a function name you have to press <Ctrl-Space>
YCM-Generator didn't do the job, so I modified the example file myself following the comments.
If you are used to Visual Assist, the auto complete works but it's really weak if compared to VA, which is a shame... I really hope someone port that plugin to Linux.
Should a daemon on an embedded device using Busybox be written in C or as a script?
All the examples I have seen use #! /bin/ash at the top of the file and that is for scripting? But in the device I'm writing to has only complied C files (I think) and symbolic links in /usr/bin.
Every way I try to compile a C file with #include </bin/ash> (e.g. gcc -Wall -o daemon_busybox daemon_busybox.c) I get error after error report in /bin/ash:
/bin/ash:174:1: error: stray ‘\213’ in program
/bin/ash:174:1: error: stray ‘\10’ in program
/bin/ash:174:1: error: stray ‘\273’ in program
/bin/ash:174:1: error: stray ‘\204’ in program
/bin/ash:174:1: error: stray ‘\342’ in program
Note I have set this: /bin/ash -> busybox
Any ideas which way I should go?
Update:
I've been given the task trying to see if a daemon can be run on a small device that runs Linux (2.6.35-at-alpha4) and Java (SE Embedded Runtime Environment) with very limited memory (i.e. a 10 second wait to get java -version to report back).
Two weeks ago I didn't know much about daemons — only knew the word. So, this is all new to me.
On my development machine I have built two different daemon files, one in C and one as a script. Both run very nicely on my Linux machine.
But because of the very small size of the target device there is only busybox (no /lib/lsb/init-functions). So I'm trying to build a 3rd daemon file. I believe it should be written in C for this device, but all examples for busybox point to scripting.
Once your question is edited so that the file name you're trying to #include is visible, the problem becomes self-evident:
#include </bin/ash>
This tries to make the C compiler include the binary of busybox (via the symlink /bin/ash) into the code to be compiled. The average binary is not a valid C source file; this is doomed to failure.
Perhaps you simply need to drop that line — the C compiler stands a better chance of working if it is given header files and source files to compile. Maybe there's more work needed; we don't have enough information to help there.
Many daemons are written as C programs, but a carefully written shell script could be used instead.
Personally, I would like to do this as a script (I've never liked C). But on the device everything in the /usr/sbin folder looks like a C file. So, the conservative coder in me says C is the way to go. I know: ask the guys developed the device — but they're long gone. Right now my daemon is just a test (i.e. printf("Hello World\n"); ). I'm trying to get printf passed to Busybox. But so far I cannot get this file to compile. I just need a simple daemon in C to start.
OK; your C code for that should be just:
#include <stdio.h>
int main(void)
{
printf("Hello World\n");
return 0;
}
Save it in hw_daemon.c. Compile it using:
gcc -o hw_daemon hw_daemon.c
If that won't compile, then you've not got a workable C development environment for the target machine. If that will compile, you should be able to run it with:
./hw_daemon
and you should see the infamous 'Hello World' message appear.
If that does not work, then you can go with the script version instead, in a file hw_script.sh:
#!/bin/ash
printf "Hello World\n"
You should be able to run that with:
Predicted output — not output observed on a machine.
$ ash hw_script.sh
Hello World
$ chmod +x hw_script.sh
$ ./hw_script.sh
Hello World
$
If neither of those works at all, then you've got major problems on the system (maybe Busybox doesn't provide a printf command workalike, for example, and you need to use echo "Hello World" instead of the printf).
This may be compiler specific, in which case I am using the IAR EWARM 5.50 compiler (firmware development for the STM32 chip).
Our project consists of a bunch of C-code libraries that we compile first, and then the main application which compiles its C-code and then links in those libraries (pretty standard stuff).
However, if I use a hex editor and open up any of the library object files produced or the final application binary, I find a whole bunch of plain text references inside the output binary to the file paths of the C files that were compiled. (eg. I see "C:\Development\trunk\Common\Encryption\SHA_1.c")
Two issues with this:
we don't really want the file paths being easily readable as that indicates our design some what
the size of the binary grows if you have your C-files located in a long subdirectory (the binary contains the full path, not just the name)...this is especially important when we're dealing with firmware that has a limited amount of code space (256KB).
Any thoughts on this? I've tried all the switches in the compiler I can think of to "remove debug information", etc., but those paths are still in there.
"The command-line option --no_path_in_file_macros has been added. It removes the path leaving only the filename for the symbols FILE and BASE_FILE."
It is defined in the release notes if IAR.
http://supp.iar.com/FilesPublic/UPDINFO/005832/arm/doc/infocenter/iccarm_history.ENU.html
Or you can look for FILE and BASE_FILE macros and remove it you do not want to use the flag.
I just started to learn masm32 and am a bit confused about the .obj files, I used C# before, so the compiler linked for me, now I have qeditor but I cant find an option to assemble multiple .asm files. I have a very basic program built of:
Vector.asm (+ Vector.inc), ...is a vector
Matrix.asm (+ Matrix.inc), ...is a matrix
Main.asm ... is the main program where I do some Vector calculations
When I compile each one of them seperate, I get 3 .obj files, what are they? I looked into the makeit.bat at the line:
\masm32\bin\PoLink /SUBSYSTEM:CONSOLE "console.obj"
so I thought I could just change it to
\masm32\bin\PoLink /SUBSYSTEM:CONSOLE "console.obj" "vector.obj" "matrix.obj"
to compile my whole program, but I was wrong :(, can anyone help me to successfully create a .bat (because maybe I want to create a little ide later, for which I would need a .bat) which compiles the 3 .obj files into 1 .exe?
I'm not familiar with PoLink, but a standard linker requires more than just a list of .obj files. It will also need to know what you intend on calling the resulting .exe (it can assume if you only give it a single .obj file). May also require an entry point. May even require library definitions if you're doing multiple files. You really need to read the docs and see what it wants on the command line...