gdb print static variable from function

Question

We have a C++ program such as:

int&
Instance()
{
    static int test;
    return test;
}

int
main( int argc, char ** argv )
{
    int& test = Instance();
    printf("%d\n",test);
    
    return 0;
}

Now I'm trying to print Instance::test, as suggested by some gdb documentation: https://ftp.gnu.org/old-gnu/Manuals/gdb/html_node/gdb_52.html

However, this yields:

(gdb) p Instance::test

No symbol "test" in specified context.

I'm compiling with -O0 -g.

I'm wondering whether it's undefined behavior to pass references to a function printf that knows nothing about what a reference is. It just seems wrong to me. I'll stick my neck out -- I don't have the C++ spec in front of me right now, but I'm hedging my bet that the code has undefined behavior due to passing a reference to printf() — PaulMcKenzie
– PaulMcKenzie, Commented Aug 12, 2014 at 21:30
Why wouldn't it be fine? I'm using a reference which will result in a copy of an integer. The only issue that I could see is with the vararg implementation. In my experience and this example, it works fine. But this is also not the question at hand — Sioux
– Sioux, Commented Aug 14, 2014 at 2:52
The only issue that I could see is with the vararg implementation Which was my point. Plus, comments are meant for comments, that's I didn't post my comment as an answer. — PaulMcKenzie
– PaulMcKenzie, Commented Aug 14, 2014 at 3:00

Jordan Samuels · Accepted Answer · 2014-08-12 21:21:17Z

16

(gdb) p 'Instance()::test'

works for me on Ubuntu 14.04, gdb 7.7, g++ 4.8.2 . How did I know that was the symbol?

$ nm -C a.out | grep test
0000000000601040 d Instance()::test

answered Aug 12, 2014 at 21:21

Jordan Samuels

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5 Comments

Sioux Over a year ago

Correct. The key is the single quotes.

Jordan Samuels Over a year ago

@Sioux Yes - I should have called attention to that from the beginning.

Baruch Over a year ago

I was having a similar problem, and your nm trick solved it for me. However, the symbol was prevRev.6906. It worked, but what is this symbol, and how was I supposed to guess it?

Jordan Samuels Over a year ago

@baruch what compiler, version, and flags are you using? And are you compiling the code in the original question, or other code?

Baruch Over a year ago

Other code. gcc (mingw64) 4.9.2, -g. In my code, the static variable scope is not directly in a function, but rather in an inner block (it is declared within an if block)

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