I am writing a program using the Contiki operating system.
I have the remote_firmware.c file and a folder called parser with the files parser.h and parser.c where I wrote the method void test(). I included parser.h in remote_firmware.c with:
#include "parser/parser.h"
The Makefile looks like this:
CONTIKI_PROJECT = remote_firmware
all: $(CONTIKI_PROJECT)
#UIP_CONF_IPV6=1
CONTIKI_WITH_RIME = 1
CONTIKI = $(HOME)/contiki
include $(CONTIKI)/Makefile.include
When I try to build this the Error occurs:
undefined reference to 'test'
I am aware that the Makefile needs to know about parser.h, but I do not know how. I tried several solutions which were proposed here but I guess I did something wrong. Maybe somebody of you know what to do?
Thank you a lot.
Where is your source file located? Try adding the source file name to the PROJECT_SOURCEFILES preprocessor variable (i.e PROJECT_SOURCEFILES+=parser.c) and adding the location of the source file to the CONTIKIDIRS preprocessor variable (i.e CONTIKIDIRS+={Directory}).
If parser.c depends on a lot other C files you might want create an C library archive first and then adding the library to your project by adding the name of the library to the TARGET_LIBFILES variable.
The error undefined reference to test is an error from the linker not the compiler. It has nothing to do with including a header file. It means when you linked the executable you didn't include parser.o
Related
I have created a library in C and want to link it when compiled. Do I have to save in a certain folder in my computer's file system or can I create my own file structure within my application to save it?
Update: My error turned out to be not properly including a header file. My files and linker were fine but it was simple syntax error.
You can save it wherever you want. Just make sure that the compiler knows the location. In the case of gcc for example, you can use:
gcc -L path/to/libdir -l:mylib.a ...
(assuming mylib.a is in path/to/libdir)
Or even:
gcc path/to/libdir/mylib.a ...
I did setup a C project with Eclipse Photon (4.8.0) for developing a program for the ESP-32. I did configure the IDE according to this official setup instructions.
Flashing the ESP-32 works fine. But as soon as I try to include header files from a sub folder, I run into troubles. I have set up a very simple project to illustrate the issue. The project consists of main.c, base/test.h and base/test.c, whereas the test.h and test.c files only contain one function with the signature void function1(void);.
When I try to call function1() in main.c, I get this error in main.c:
Undefined reference to function1()
Please compare to the attached screenshot, where everything is depicted.
How to solve this issue?
This is not a compiler, but rather a linker error.
Note, with #includeing a header file, you only make the external function known to the compiler. You also need to link to the external function during the linking stage. Make sure you include the compiled object file that contains function1 into the link.
Seems like you need to do proper linking.
If you are linking with a library, you need to specify:
The name of the library: Project\Settings\C C++ General\Paths and Symbols\Libraries
Location where the linker should search for this library:
Project\Settings\C C++ General\Paths and Symbols\Library Paths
Important: see Note.
If you are linking with object files, add those to:
Project\Settings\C C++ Build\Settings\Linker\Miscellaneous\Other objects
Note:
If your library name is, for example, libsomething.a, than you need to specify only something as the name; so omit lib prefix and .a suffix.
If your library is not prefixed with lib, then you need to add its name prefixed with :. For example, something.a should be added as :something.a.
Imagine that I have a C-project in the following folder:
C:\microcontroller\stm32\myProject
I have two important folders inside myProject:
- source => here are all my .c and .h files
- build => gcc will write all the object files in here
Note: as you can see, the backward slashes indicate that this is happening on a Windows pc.
The figure below gives an overview:
I will not display my complete makefile here, because that would lead us too far. The rules inside the makefile for all .c => .o files are similar. Let us just focus on the compilation of one specific file: fileA2.c:
--------------------- COMPILATION OF FILE fileA2.c -------------------
Building ./build/folderA/fileA2.o
arm-none-eabi-gcc C:\\microcontroller\\stm32\\myProject\\source\\folderA\\fileA2.c
-o C:\\microcontroller\\stm32\\myProject\\build\\folderA\\fileA2.o
-c
-MMD
-mcpu=cortex-m7
-...
-IC:/microcontroller/stm32/myProject/source/folderA
-IC:/microcontroller/stm32/myProject/source/folderB
Notice that the gcc call ends with two include flags: one for folderA and one for folderB. This enables gcc to use any of the header files from these folders (fileA1.h, fileA2.h or fileB1.h) if fileA2.c has an import statement.
Let us now consider the source code in fileA2.c. We assume that this file needs to include fileA2.h and also fileB1.h.
/*******************************/
/* SOURCE CODE fileA2.c */
/*******************************/
// Some include statements
#include "fileA2.h"
#include "fileB1.h"
// Code
...
These include statements work perfectly. The gcc compiler retrieves the files fileA2.h and fileB1.h in the given folders. But I noticed that the following does not work:
/*******************************/
/* SOURCE CODE fileA2.c */
/*******************************/
// Some include statements
#include "fileA2.h"
#include "folderB/fileB1.h"
// Code
...
The last include statement is a 'partial path' to the file. I get the error when compiling:
fatal error: folderB/fileB1.h: No such file or directory
How can I get gcc to handle this?
PS: It is not my own habit to use 'partial paths'. But they appear a lot in the libraries from the silicon vendor of my chip, so I have to live with it.
You specify two paths to look for includes other than the current directory for the source file:
-IC:/microcontroller/stm32/myProject/source/folderA
-IC:/microcontroller/stm32/myProject/source/folderB
You get the error because neither
C:/microcontroller/stm32/myProject/source/folderA/folderB/fileB1.h nor
C:/microcontroller/stm32/myProject/source/folderB/folderB/fileB1.h exists.
To address the error, you can add the following path:
-IC:/microcontroller/stm32/myProject/source
When using double-quotes to include a header file the compiler first looks in the same directory as the current file. If the header file is not found then it continues with the standard include search paths.
So when the compiler compiles the file source/folderA/fileA2.c the first directory the compiler will look for include files is the source/folderA directory. In the first example the fileB1.h will not be found there, but since you added source/folderB to the standard search path it will be found there as source/folderB/fileB2.h.
In the second example there is no folderB/fileB1.h file on source/folderA so the compiler will search the standard search path. When it comes to source/folderB it will again try folderB/fileB2.h (i.e. source/folderB/folderB/fileB2.h) and it will still not be found, nor will it be found anywhere else.
You need to add -IC:/microcontroller/stm32/myProject/source to be able to find folderB/fileB1.h.
Apart of the two correct responses you have received before this, you have the third chance to specify the path to the file in the #include directive from the curren directory, as with
`#include "../folderB/fileB1.h"
I've taken the plunge and am learning C. It's been a pretty good but manageable learning curve coming from a scripting (php, perl) background with only a little bit of C#.
I've used the web-site "Learn C The Hard Way" and am so far grasping reasonably well (I think) but I can't understand this part of one of the exercises:
http://c.learncodethehardway.org/book/ex19.html
He created four source files - object.h, object.c, ex19.h, ex19.c
But I don't understand how the object.c file is included.
The main function is located in ex19.c, and it has the line
#include "ex19.h"
File ex19.h has the line
#include "object.h"
But object.h makes no reference to including object.c. Interestingly object.c contains the line
#include "object.h"
Is there some sort of implied include where if you include the header file, it will automatically include the c source code of the same name?
This is the job of a separate program called the linker. In C, source files need access to the header files of other C source files so that they can see information about what functions, types, and variables are defined by that second C file that the first file might want to use. Each C file is then compiled independently of the rest. The output of the compiler is an object file.
To build a final program, a second program called the linker comes in and combines all the object files together into the overall executable. This program is tasked with taking the implementations of all the different C files and cross-referencing them against one another so that each time one C file references a function or variable in a different C file, that reference can actually be made to the appropriate object.
This is why you don't need to include .c files. Once a source file has a header, it knows enough about the other file in order to use the functions it provides for the compiler to verify that it's using them correctly. The linker then handles of the job of actually making the cross-references. You can think of the compiler as a program that checks to see that if the functions are defined, then the program would work. The linker then actually checks to make sure that those functions are defined in the first place and sets up the appropriate links in the executable.
Hope this helps!
Object.c is not included.
It's compiled as it's own unit and it includes object.h
See the make file:
CFLAGS=-Wall -g
all: ex19
ex19: object.o
clean:
rm -f ex19
ex19: object.o tells you that object.o must be created before ex19 can be built, and this is picked up by default from make file as an object.c exists.
So this make file says
to build all you need ex19, to get ex19 you need object.o, and the to create object.o the makefile picks up object.o built from the object.c
From the page you reference:
make can't see anything in the file for object.o, but it does see an
object.c file, and it knows how to turn a .c into a .o, so it does
that.
The entire logic lies in the makefile and an intelligent compiler. The final binary created has an object file named as object.o which will ideally contain all the function definitions defined in object.h file. It is the linker which links the functions declared in .h file with the definition which are available in .o file.
This has gotten a bit lost in translation so I am going to be more precise:
we have classes recursion.c, fib.c, and countUp.c. from recursion.c we have to recursively call fib.c or countUp.c, decided by the input argument. I can't use header files and am only given that I must place prototypes:
int fib(int n);
and
void countUp(int n);
My Makefile
TAR = tar
COMPILER_FLAGS = -g -Wall -std=c99 -c
LINKER_FLAGS = -g -o
OBJS = recurse.o
C_FILES = recurse.c fib.c countUp.c
ASM_FILES = recurse.asm
TARGET_FILE = recurse
TARGET_TAR = PA5.tar
$(TARGET_TAR): $(TARGET_FILE)
$(TAR) -cvf $(TARGET_TAR) $(C_FILES) $(ASM_FILES) $(TARGET_FILE) Makefi$
recurse.o: recurse.c
$(C_COMPILER) $(COMPILER_FLAGS) $(C_FILES)
$(TARGET_FILE): $(OBJS)
$(LD_LINKER) $(LINKER_FLAGS) $(TARGET_FILE) $(OBJS)
where fib and countUp class methods must be called recursively. The recursive.c file is considered our c driver. Do not create or implement any header files OTHER than those that are standard c headers (stdio.h, string.h, etc.). When I try to run this I get:
make
gcc -g -o recurse recurse.o
recurse.o: In function `main':
(file root location)/recurse.c:43: undefined reference to `fib'
(file root location)/recurse.c:46: undefined reference to `countUp'
collect2: ld returned 1 exit status
make: *** [recurse] Error 1
Any clue what is going on.
Original Question:
I have multiple C files that I am combining into an executable. For example say I have math.c, the arguments are passed into it, and then if the input argument calls add it performs functions from add.c, if the argument calls subtract it will call functions from subtract.c, etc. The files are then compiled into a .o file, and then an executable is created. The issue I have is not being able to utilize header (.h) files. Is there any way to break into the separate classes or am I missing something? I really don't know exactly how to ask the question, jargon is pretty bad as far as C goes, sorry :(
I don't really get the idea of a driver I guess. (Not a device driver, she keeps telling us this is a c executable driver).
If I understood correctly, what I think you need to do is add the following prototypes above any of the functions you define in recursion.c. The prototypes will allow you to call these functions from within any function inside recursion.c (In fact, including a header file is akin to copy-pasting all of the prototypes defined in the file, as #Justin and #EdS already pointed out)
int fib(int n);
void countUp(int n);
int main() {
...
}
Then you need to make sure that your project file includes the files recursion.c, fib.c, and countUp.c - When you build your project, the linker will do its job and lookup the entry points in your compiled object files, and will proceed to assemble a single executable file.
What compiler are you using?
Including a header file is just a preprocessor directive to include the contents of that file at the location of the include. To achieve the same thing without a header file just copy and paste the code that you would have put in the header file into the top of each c file.
Of course this isn't very maintainable as if you want to change that contents you need to change it in many files, hence why header files exist in the first place.
Since this is homework and considering the fact that you have told us that A) You have no header files to use, and B) you have not been instructed to utilize the extern keyword, it seems to me that your only choice is to include the .c files themselves:
#include "add.c"
#include "subtract.c"
/* etc... */
int main()
{
// use functions defined in "add.c", "subtract.c", etc.
}
Note that this is bad form as you are including the implementation instead of the interface and likely pulling in a bunch of stuff you don't want or need. If that doesn't answer your question then there is something, some instruction from your teacher, missing in the question.