I want make wrapper for another shared library.
elsymobileclient.h
extern void* CreateClass(void);
elsymobileclientwrapper.c
#include <AnswStruct.h>
#include <elsymobileclient.h>
void * W_CreateClass() {
return CreateClass();
}
compile:
$ gcc -I. -L. elsymobileclientwrapper.c -lelsymobileclient
/tmp/ccDxlXsd.o: In function W_CreateClass':
elsymobileclientwrapper.c:(.text+0x7): undefined reference toCreateClass'
collect2: ld returned 1 exit status
Where's wrong?
Related
How do I prevent namespace collisions in a library? Let's say I have a internal library function called foo(), that is not included in a public header, so the user doesn't know about this function. But foo() is used across multiple files and can't be declared static.
The Problem is, if the user now creates a function called foo(), there is an error. How do I prevent namespace collision (as the library author), without forcing the user to not use specific function names?
example.c
#include <stdio.h>
void foo() {
printf("my foo called");
}
int main() {
foo();
}
lib.c
#include <stdio.h>
void foo() {
printf("library foo() called\n");
}
output:
$ gcc -Wall -Wextra -Werror example.c example-lib.c
/usr/bin/ld: /tmp/cci3Dd3J.o: in function `foo':
example-lib.c:(.text+0x0): multiple definition of `foo'; /tmp/ccneOJjI.o:example.c:(.text+0x0): first defined here
collect2: error: ld returned 1 exit status
Edit
I now tried the following (with the same files):
$ gcc -Wall -Wextra -Werror example-lib.c -fpic -shared -o example-lib.so
$ gcc -Wall -Wextra -Werror example.c example-lib.so
And for some reason it works. Can anyone explain why?
i'm trying to include all SDL libraries that i have already installed and exist in '/usr/include/SDL' this directory contains all .h files
#include <SDL/SDL.h>
#include <stdio.h>
#include <stdlib.h>
int main ()
{
SDL_Surface *screen=NULL ;
SDL_Init (SDL_INIT_VIDEO);
if (SDL_Init(SDL_INIT_VIDEO !=0))
{
printf("erreur");
return 1 ;
}
screen=SDL_SetVideoMode (400,400,32,SDL_HWSURFACE | SDL_DOUBLEBUF);
if (screen== NULL)
{
printf("Unable to set video mode : %s \n",SDL_GetError() );
return 1;
}
SDL_Flip (screen);
SDL_Quit ();
return 0;
}
when i compile code above that exists in main.c in terminal using this command:
gcc main.c -o program -LSDL
i get this :
axemaster#ubuntu:~/Desktop/stackoverflow$ gcc main.c -o program -LSDL
/tmp/ccMx1per.o: In function `main':
main.c:(.text+0x16): undefined reference to `SDL_Init'
main.c:(.text+0x20): undefined reference to `SDL_Init'
main.c:(.text+0x53): undefined reference to `SDL_SetVideoMode'
main.c:(.text+0x63): undefined reference to `SDL_GetError'
main.c:(.text+0x88): undefined reference to `SDL_Flip'
main.c:(.text+0x8d): undefined reference to `SDL_Quit'
collect2: error: ld returned 1 exit status
How can i solve this ?
I have a very simple code:
#include <openssl/sha.h>
int main() {
SHA_CTX sha1;
SHA_Init(&sha1);
}
I have installed both libssl-dev and libcrypto++-dev:
However I have a build failure using the following command:
$ gcc -lcrypto -lssl main.c
/tmp/ccfnCAxT.o: In function `main':
main.c:(.text+0x1f): undefined reference to `SHA1_Init'
collect2: error: ld returned 1 exit status
$
$ gcc -lssl main.c
/tmp/ccfnCAxT.o: In function `main':
main.c:(.text+0x1f): undefined reference to `SHA1_Init'
collect2: error: ld returned 1 exit status
Platform: Ubuntu 16.04
-lssl is not needed, -lcrypto is enough, and it must be at the end:
gcc -o main main.c -lcrypto
(or whatever you want your program to be called goes after -o)
I made a shared library as the follow:
gcc -c output.c
gcc -shared -fPIC -o liboutput.so output.o
When output.c is the follow, it could work.
//#include "output.h"
#include <stdio.h>
int output(const char* st) {
return 1+2;
}
But, when output.c changed as the follow, a error occur.
//#include "output.h"
#include <stdio.h>
int output(const char* st) {
printf("%s\n", st);
return 1+2;
}
This is error message:
/usr/bin/ld: output.o: relocation R_X86_64_PC32 against undefined 符号 `puts##GLIBC_2.2.5' can not be used when making a shared object; recompile with -fPIC
/usr/bin/ld: 最后的链结失败: 错误的值
collect2: error: ld returned 1 exit status
I want to know why and how to deal it. Thanks in advance.
You need to compile output.c as position independent code.
gcc -c -fPIC output.c
In the first version you have not called any library function. But in second one printf is being called. In general, compile all sources with -fPIC if you intend to build a shared library later.
I am using Cygwin environment with Lua Interpreter package included while cygwin installation.
So I am able to compile and run sample lua progs.
But when i try to execute a sample c file which has lua calls , i am always getting this following error.
$ cc -o ../samples/ctest -Wall ../samples/ctest.c
/tmp/ccOYgLj4.o:ctest.c:(.text+0x2b): undefined reference to `_luaL_newstate'
/tmp/ccOYgLj4.o:ctest.c:(.text+0x3d): undefined reference to `_luaL_openlibs'
/tmp/ccOYgLj4.o:ctest.c:(.text+0x59): undefined reference to `_luaL_loadfile'
/tmp/ccOYgLj4.o:ctest.c:(.text+0x82): undefined reference to `_lua_pcall'
/tmp/ccOYgLj4.o:ctest.c:(.text+0xb8): undefined reference to `_lua_getfield'
/tmp/ccOYgLj4.o:ctest.c:(.text+0xd5): undefined reference to `_lua_call'
/tmp/ccOYgLj4.o:ctest.c:(.text+0xf0): undefined reference to `_lua_close'
collect2: ld returned 1 exit status
My sample ctest.c file contents:
#include <stdio.h>
#include "lua.h"
#include "lualib.h"
#include "lauxlib.h"
/* lua interpreter */
lua_State* l;
int main () {
int dofile;
/* initialize lua */
l = lua_open();
/* load lua libraries */
luaL_openlibs(l);
/* run the hello.lua script */
dofile = luaL_dofile(l, "hello.lua");
if (dofile == 0) {
/* call foo */
lua_getglobal(l,"foo");
lua_call(l,0,0);
}
else {
printf("Error, unable to run hello.lua\n");
}
/* cleanup Lua */
lua_close(l);
return 0;
}
hello.lua file contents:
print("from c hurray")
on searching the net everywhere they say some linker error and have to include -llua51. So i tried the following .
$ cc -o ../samples/ctest -Wall -llua5.1 ../samples/ctest.c
/tmp/cc3v5Nim.o:ctest.c:(.text+0x2b): undefined reference to `_luaL_newstate'
/tmp/cc3v5Nim.o:ctest.c:(.text+0x3d): undefined reference to `_luaL_openlibs'
/tmp/cc3v5Nim.o:ctest.c:(.text+0x59): undefined reference to `_luaL_loadfile'
/tmp/cc3v5Nim.o:ctest.c:(.text+0x82): undefined reference to `_lua_pcall'
/tmp/cc3v5Nim.o:ctest.c:(.text+0xb8): undefined reference to `_lua_getfield'
/tmp/cc3v5Nim.o:ctest.c:(.text+0xd5): undefined reference to `_lua_call'
/tmp/cc3v5Nim.o:ctest.c:(.text+0xf0): undefined reference to `_lua_close'
collect2: ld returned 1 exit status
Vedhashree#Vedhashree-PC /cygdrive/c/cygwin/bin
$ ls /usr/lib/liblua*.a
/usr/lib/liblua.a /usr/lib/liblua5.1.a
/usr/lib/liblua.dll.a /usr/lib/liblua5.1.dll.a
Can you help me fix this issue and make my first embedded lua c program work?
Update:
$ cc -o ctesing -Wall ctesting.c -llua5.1
/usr/lib/gcc/i686-pc-cygwin/4.3.4/../../../../i686-pc-cygwin/bin/ld: cannot find
-llua5.1
collect2: ld returned 1 exit status
-----------------------------------------------------------------
cc -o ../samples/ctest -Wall ../samples/ctest.c -llua
/usr/lib/gcc/i686-pc-cygwin/4.3.4/../../../../i686-pc-cygwin/bin/ld: cannot find
-llua51
collect2: ld returned 1 exit status
-----------------------------------------------------------------
cc -o ../samples/ctest -Wall ../samples/ctest.c -llua51
/usr/lib/gcc/i686-pc-cygwin/4.3.4/../../../../i686-pc-cygwin/bin/ld: cannot find
-llua
collect2: ld returned 1 exit status
-----------------------------------------------------------------
Still I get only these errors :(
Place -llua5.1 after ../samples/ctest.c. Objects should be linked in reverse order of dependency.
cc -o ../samples/ctest -Wall ../samples/ctest.c -llua5.1
UPDATE: Your update describes a different problem. In this case the linker cannot find a liblua5.1.a file in its search path. Make sure that you have such a library on your system and try adding its path using the -L option.