Linker Error on Linux: "Undefined Reference To"

Linker error on Linux: undefined reference to

Put the libraries after the object files on the link command line:

gcc /media/sf_BitEagle_Projects/cbitcoin/build/obj/testCBAddress.o \
    /media/sf_BitEagle_Projects/cbitcoin/build/obj/CBOpenSSLCrypto.o \
    -L/media/sf_BitEagle_Projects/cbitcoin/build/bin \
    -lcbitcoin -Wl-rpath,/media/sf_BitEagle_Projects/cbitcoin/build/bin \
    -L/usr/local/ssl/lib/ -lssl -lcrypto \
    -o /media/sf_BitEagle_Projects/cbitcoin/build/bin/testCBAddress

If you don't do that, the linker may decide that it needs nothing from a particular library at the stage of the link where it scans the library, and then it won't rescan the library later after it finds some undefined symbols in the object files. If you put the object files first, you don't run into this problem.

Linker error : undefined reference to _fbss

I resolve the problem in this way.

Actually Here is the solution.

I'm not accurate but I think the problem is that the name is not matched.
crt0, which seems to be the helper of start riscv processor has this line la a0 _fbss just basically linker can recognize this if _fbss is replaced with _edata. So i edit the assembly file which is located at pulp-riscv-gnu-toolchain/riscv-newlib/libgloss/riscv/ And rebuild the gnu toolchain. And execute your compiler with -T option like riscv32-unknown-elf-g++ -o main main.cpp -T /home/jskim/test_toolchains/riscv32-unknown-elf-ld/lib/ldscripts/elf32lriscv.x

This is the easiest solution as I think.

Linker error - undefined reference -gcc

gcc -c arrayImpl.c -o arrayImpl.o

That is missing -DARRAY. Without that the code in arrayImpl.c is conditionally removed:

/***************** arrayImple.c **************/

#if defined(ARRAY)

Linker Error: Undefined Reference to Function

That sounds like a very old gcc compiler. That was a problem during abi change in earlier versions of gcc and installed libraries on the system.

using -D_GLIBCXX_USE_CXX11_ABI=0 and recompile all maybe help.

See also this documentation:
https://gcc.gnu.org/onlinedocs/libstdc%2B%2B/manual/using_dual_abi.html

BTW:
I can compile and link your code with gcc 7.3.1 ( fedora ) without any error. Some warnings of unused vars after cut and paste your code and only add an empty aBoard class. So I believe there is nothing wrong with your code.

From the documentation:

If you get linker errors about undefined references to symbols that involve types in the std::__cxx11 namespace or the tag [abi:cxx11] then it probably indicates that you are trying to link together object files that were compiled with different values for the _GLIBCXX_USE_CXX11_ABI macro. This commonly happens when linking to a third-party library that was compiled with an older version of GCC. If the third-party library cannot be rebuilt with the new ABI then you will need to recompile your code with the old ABI.

What is an undefined reference/unresolved external symbol error and how do I fix it?

Compiling a C++ program takes place in several steps, as specified by 2.2 (credits to Keith Thompson for the reference):

The precedence among the syntax rules of translation is specified by the following phases [see footnote].

1. Physical source file characters are mapped, in an implementation-defined manner, to the basic source character set
   (introducing new-line characters for end-of-line indicators) if
   necessary. [SNIP]
2. Each instance of a backslash character (\) immediately followed by a new-line character is deleted, splicing physical source lines to
   form logical source lines. [SNIP]
3. The source file is decomposed into preprocessing tokens (2.5) and sequences of white-space characters (including comments). [SNIP]
4. Preprocessing directives are executed, macro invocations are expanded, and _Pragma unary operator expressions are executed. [SNIP]
5. Each source character set member in a character literal or a string literal, as well as each escape sequence and universal-character-name
   in a character literal or a non-raw string literal, is converted to
   the corresponding member of the execution character set; [SNIP]
6. Adjacent string literal tokens are concatenated.
7. White-space characters separating tokens are no longer significant. Each preprocessing token is converted into a token. (2.7). The
   resulting tokens are syntactically and semantically analyzed and
   translated as a translation unit. [SNIP]
8. Translated translation units and instantiation units are combined as follows: [SNIP]
9. All external entity references are resolved. Library components are linked to satisfy external references to entities not defined in the
   current translation. All such translator output is collected into a
   program image which contains information needed for execution in its
   execution environment. (emphasis mine)

[footnote] Implementations must behave as if these separate phases occur, although in practice different phases might be folded together.

The specified errors occur during this last stage of compilation, most commonly referred to as linking. It basically means that you compiled a bunch of implementation files into object files or libraries and now you want to get them to work together.

Say you defined symbol a in a.cpp. Now, b.cpp declared that symbol and used it. Before linking, it simply assumes that that symbol was defined somewhere, but it doesn't yet care where. The linking phase is responsible for finding the symbol and correctly linking it to b.cpp (well, actually to the object or library that uses it).

If you're using Microsoft Visual Studio, you'll see that projects generate .lib files. These contain a table of exported symbols, and a table of imported symbols. The imported symbols are resolved against the libraries you link against, and the exported symbols are provided for the libraries that use that .lib (if any).

Similar mechanisms exist for other compilers/ platforms.

Common error messages are error LNK2001, error LNK1120, error LNK2019 for Microsoft Visual Studio and undefined reference to symbolName for GCC.

The code:

struct X
{
   virtual void foo();
};
struct Y : X
{
   void foo() {}
};
struct A
{
   virtual ~A() = 0;
};
struct B: A
{
   virtual ~B(){}
};
extern int x;
void foo();
int main()
{
   x = 0;
   foo();
   Y y;
   B b;
}

will generate the following errors with GCC:

/home/AbiSfw/ccvvuHoX.o: In function `main':
prog.cpp:(.text+0x10): undefined reference to `x'
prog.cpp:(.text+0x19): undefined reference to `foo()'
prog.cpp:(.text+0x2d): undefined reference to `A::~A()'
/home/AbiSfw/ccvvuHoX.o: In function `B::~B()':
prog.cpp:(.text._ZN1BD1Ev[B::~B()]+0xb): undefined reference to `A::~A()'
/home/AbiSfw/ccvvuHoX.o: In function `B::~B()':
prog.cpp:(.text._ZN1BD0Ev[B::~B()]+0x12): undefined reference to `A::~A()'
/home/AbiSfw/ccvvuHoX.o:(.rodata._ZTI1Y[typeinfo for Y]+0x8): undefined reference to `typeinfo for X'
/home/AbiSfw/ccvvuHoX.o:(.rodata._ZTI1B[typeinfo for B]+0x8): undefined reference to `typeinfo for A'
collect2: ld returned 1 exit status

and similar errors with Microsoft Visual Studio:

1>test2.obj : error LNK2001: unresolved external symbol "void __cdecl foo(void)" (?foo@@YAXXZ)
1>test2.obj : error LNK2001: unresolved external symbol "int x" (?x@@3HA)
1>test2.obj : error LNK2001: unresolved external symbol "public: virtual __thiscall A::~A(void)" (??1A@@UAE@XZ)
1>test2.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall X::foo(void)" (?foo@X@@UAEXXZ)
1>...\test2.exe : fatal error LNK1120: 4 unresolved externals

Common causes include:

• Failure to link against appropriate libraries/object files or compile implementation files
• Declared and undefined variable or function.
• Common issues with class-type members
• Template implementations not visible.
• Symbols were defined in a C program and used in C++ code.
• Incorrectly importing/exporting methods/classes across modules/dll. (MSVS specific)
• Circular library dependency
• undefined reference to `WinMain@16'
• Interdependent library order
• Multiple source files of the same name
• Mistyping or not including the .lib extension when using the #pragma (Microsoft Visual Studio)
• Problems with template friends
• Inconsistent UNICODE definitions
• Missing "extern" in const variable declarations/definitions (C++ only)
• Visual Studio Code not configured for a multiple file project

OpenGL on Arch Linux - Linker Error: Undefined Reference

Your compilation is not complete, you only try to compile one file, whereas there is several.

You can use theses command to compile :

# compile the C file
gcc -c -Wall glad.c -I lib/include/

# compile the c++ files 
g++ -c -Wall -I lib/include EBO.cpp
g++ -c -Wall -I lib/include main.cpp
g++ -c -Wall -I lib/include shaderClass.cpp
g++ -c -Wall -I lib/include VAO.cpp
g++ -c -Wall -I lib/include VBO.cpp

# link the object files
g++ -o demo EBO.o glad.o main.o shaderClass.o VAO.o VBO.o -lglfw -ldl
 

Or you could use some Makefile:

CFLAGS= -C -Wall  -I lib/include
CXXFLAGS= -C -Wall  -I lib/include
LDFLAGS= -lglfw -ldl

CC=gcc
CXX=g++

all: demo

.PHONY: clean

clean:
    rm *.o

glad.o: glad.c 
    $(CC) $(CFLAGS) $< -c -o $@

%.o: %.c 
    $(CXX) $(CXXFLAGS) $< -c -o $@

demo: EBO.o glad.o main.o shaderClass.o VAO.o VBO.o
    $(CXX) $^ -o $@ $(LDFLAGS)

and type make to compile

Linker error on GLFW on linux (x11)

Order of libraries matter. If library A depends on library B, then A must come before B on the command line.

In your case, since the glfw3 library depends on the dl library, you must switch order so that glfw3 comes before dl on the command line.

You also must link with the X11 library.

So the full command line should look something like

g++ -o bin/Debug/Game obj/Debug/main.o -lglfw3 -ldl -lm -lGL -lGLU -lX11

How to make linker fail for undefined references when building shared library in Linux

When I'm building and want to avoid this situation, I compile the library with the options: -Wl,--no-allow-shlib-undefined -Wl,-z,defs

The first option causes the link of the shared library to fail in the situation that a symbol is not defined in the code, when used in combination with the second option, which causes the linker to report the missing symbols.

This works well to prevent missing symbols at run-time by detecting them at link time. I do, however, need to link the .so with all the libraries it uses, as otherwise it will fail to build.

sample (src.c):

#include <math.h>

extern
double share_the_stuff(double val)
{
    return acos(val * val);
}

Build with missing symbol:

gcc -shared -o src.so src.c -Wl,--no-allow-shlib-undefined -Wl,-z,defs
/usr/bin/ld: /tmp/ccFmD5uY.o: in function `share_the_stuff':
src.c:(.text+0x17): undefined reference to `acos'
collect2: error: ld returned 1 exit status

link in libm.so:

gcc -shared -o src.so src.c -Wl,--no-allow-shlib-undefined -Wl,-z,defs -lm

It behaves the same with missing internal symbols.

---

Related Topics