How to view symbols in object files?

Question

How can I view symbols in a .o file? nm does not work for me. I use g++/linux.

Wally

nm is exactly what you'd use. Can you explain how it doesn't work for you ? – Bankbook

It says : nm: Lib1.o: File format not recognized – Wally

@nakiya: Run file Lib1.o and tell us what the output is. – Smother

I built the object file straight from a header where the implementation was. Does that have anything to do with this? – Wally

@DarkDust: How to run an object file? – Wally

@Wally You can't run an .o file. And if you compile a header file you produce precompiled headers with recent gcc versions, not object files. You should compile .cpp files not header files. – Bankbook

@nakiya: You cannot run it, you should really type the text "file Lib1.o" in your shell. The tool called file tells you the file type of Lib1.o, that is whether it really is an object file. I doubt it. – Smother

Yep. :D. It says it's a precompiled header. I recompiled with implementation in a cpp file. – Wally

Answer 1

Instead of nm, you can use the powerful objdump. See the man page for details. Try objdump -t myfile or objdump -T myfile. With the -C flag you can also demangle C++ names, like nm does.

Smother

I tried ObjDump also. Same result : objdump: Lib1.o: File format not recognized – Wally

try objdump -t Lib1.o – Macintosh

Answer 2

Have you been using a cross-compiler for another platform? If so, you need to use the respective nm or objdump commmand.

For example, if you have used XXX-YYY-gcc to compile the .o file, you need to use XXX-YYY-nm or XXX-YYY-objdump to process the files.

Liddie

Answer 3

Just run: nm you_obj_file.o | c++filt

Adalai

Answer 4

There is a command to take a look at which functions are included in an object file or library or executable:

nm

Peh

The OP stated directly that he cannot use nm. – Mingmingche

@Mingmingche While that's true, I imagine some people (me at least) come to this question from just searching how to view symbols in object files, and in my case nm worked perfectly for my needs, so I think this is a fine answer given the circumstances. – Smallwood

Answer 5

You can use nm -C .o/lib/exe, for example:

xiongyu@ubuntu:~/tmp/build$ nm -C libfile1.a 

file1.cpp.o:
0000000000000000 T f()
0000000000000000 W int fun<int>(int)

using nm -C it will be more readable, if you just use nm:

xiongyu@ubuntu:~/tmp/build$ nm libfile1.a 

file1.cpp.o:
0000000000000000 T _Z1fv
0000000000000000 W _Z3funIiET_S0_

as we see it's not so readable.

Below is what my file1.cpp like:

xiongyu@ubuntu:~/tmp/build$ vi ../file1.cpp 
#include "head.h"
void f()  {
     int i = fun<int>(42);
}

Kriskrischer