I'm trying to use the library gcrypt.h but show this error:
undefined reference to `gcry_md_get_algo_dlen'
The code is:
int algo = GCRY_MD_SHA1;
unsigned int hash_len = gcry_md_get_algo_dlen(algo);
unsigned char hash[hash_len];
How can I fix it?
Make sure you have the most recent version of the library http://www.gnupg.org/download/#libgcrypt
If you have the right version make sure you added the library itself to your linker settings in Eclipse.
To do so:
Right-Click on your project -> Properties / C/C++Build / Settings / GCC C++ Linker / Libraries
There you add to libraries "gcrypt" ( you don't at the "lib" to it )
And also make sure that ( if the lib isnt under a system path ) you add the path where the library itself lies.
It looks like you are facing a Linking Error (Undefined reference to a function)
You have included the header "gcrypt.h" but the object file is not linked to your main file.
Library is NOT the same as the header (.h) file. C libraries are collections of compiled objects which are LINKED to your object code by the linker. Header files are lexically included by the preprocessor.
When you compile, you need to make sure that the libraries are where they're supposed to be AND the header files are where they're supposed to be. Either one can mess you up. Make sure that .o files are linked properly
Related
I am just starting out with Segger Embedded Studio. Right now trying to call a function of a included header file. The file seems to be included since it shows up in the dependencies. For now I simply included the header and C-File in the project directory.
The included Header- and C-Files are simply:
//##### Header-File ######
#ifndef TEST_H_
#define TEST_H_
void printText(void);
#endif //TEST_H_
and:
//###### C-File #########
#include <test.h>
#include <stdio.h>
#include <stdlib.h>
void printText(void)
{
printf("Hello");
}
But when I try to call the printText Function in my main I get the error:
"Undefined Symbol: printText".
Why is the function not recognized?
"Undefined symbol" is a linker error. You are not linking the object code containing the definition of printText().
It is not an issue with the header file; including a header file does not cause the associated code to be linked - that is just the declaration so the compiler knows what the interface looks like. It is the linker than combines the separately compiled object code to form a program. You have not told the linker to use the object code containing printText(), and you have not told your IDE project to compile it to generate that object code.
The project tree clearly shows that only main.c is included in your project; you need to add the C file containing printText() too.
The concept of separate compilation and linking is what you need to grasp here.
Thank you Clifford for your answer. You are right I had some miss-conceptions about which files will be linked while building the project. In the special case of segger embedded studio there are, as I know by now, two ways to reference extern files.
Adding the files to the sources files folder is straight forward, but must be done separately for each project you want to use the respective files.
For frequently used files it is beneficial to create a dedicated library solution. Such a library can then be imported to any solution by choosing "add existing project". This will add all files of the library to your current solution (and show them in the project-tree). Now click the tab project -> dependencies. Your library should show up here. By acitivating the check box the linker will compile the referenced project upon builing your solution, allowing for the usage of your library functions.
Adding and linking library-project to a current solution
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.
I am writing some C code in eclipse. I have some of my own header files and I put them under project properties -> GCC C Compiler -> Includes -> Include paths(-l). One of the inclded file is socket.h. When I try to compile my project compiler still points to default library (usr/includes/bits/socket.h and /usr/includes/sys/socket.h) But I have my own socket.h file which I have included under include paths(-l).
My question is, How can I restrict my compiler to point my socket.h rather than its own socket.h ? One restriction is that I cant change socket.h file name.
An easy and fast way to solve this, is to put your socket.h in a subfolder and make your include look like this:
#include "mysubfolder/socket.h"
Add the subfolders parent folder to your include paths and your done.
I'm writing some code that uses a C library provided by MATLAB (to extract data from *.mat files). In my IDE (Code::Blocks), I've included the folder containing the necessary "mat.h", which is on a network drive. My code recognises types defined in mat.h when I do this, but whenever I call functions from the file I get an "undefined reference" error. This is the same case for the example code MathWorks provides. What sort of problem usually causes this?
#include "mat.h"
int main (void) {
MATFile *pmat; // Compiles only when compiler is told to search in mat.h directory
pmat = matOpen("example_filename", "r"); // Never compiles
return 0;
}
Thanks!
Cameron
"undefined reference" is normally a linker error. It's not a problem of a header file. You need to tell the linker to link MATLAB's library (or a dedicated object) to your program.
No idea how this is done in Code::Blocks though. In the Code:Blocks documentation it is described here.
Have you checked the contents of mat.h? Does it declare matOpen()? Also, does the error occur when compiling or linking? If it's during the link phase, you probably need to reference the library that contains the implementation of matOpen() (a .lib in Windows, or .a in Unix). The .h file only declares the function.
I've added a .lib to my c project,
but still can't use things defined in that .lib in .c
main()
{
structure_defined_inthat_lib c;
...
I added that .lib this way:
Right click ,property,Linker,Input,
and in "Additional Dependencies",I type in "D:\path\name.lib"
Anything wrong?
You need to include the header files defining the stuff in that library into the code where you want to use that stuff. That header file must be on one of the paths specified in C++->General->Additional include directories - you might need to add the path to the header to that list.
Also you only specify the filename of the library in "Additional dependencies" in the linker settings and provide the path to that file in "Additional library directories".
You need both the library and the header to use the functions defined in the library. If you know the function signatures, you can also declare them using extern.