How do I examine the contents of an std::vector in gdb, using the icc compiler?

Question

I want to examine the contents of a std::vector in gdb but I don't have access to _M_impl because I'm using icc, not gcc, how do I do it? Let's say it's a std::vector for the sake of simplicity.

There is a very nice answer here but this doesn't work if I use icc, the error message is "There is no member or method named _M_impl". There appears to be a nice debug toolset here but it also relies on _M_impl.

Answer 1

Not sure this will work with your vector, but it worked for me.

#include <string>
#include <vector>

int main() {
    std::vector<std::string> vec;
    vec.push_back("Hello");
    vec.push_back("world");
    vec.push_back("!");
    return 0;
}

gdb:

(gdb) break source.cpp:8
(gdb) run
(gdb) p vec.begin()
$1 = {
   _M_current = 0x300340
}
(gdb) p $1._M_current->c_str()
$2 = 0x3002fc "Hello"
(gdb) p $1._M_current +1
$3 = (string *) 0x300344
(gdb) p $3->c_str()
$4 = 0x30032c "world"

Answer 2

Generally when I deal with the container classes in a debugger, I build a reference to the element, as a local variable, so it is easy to see in the debugger, without mucking about in the container implementation.

Here is a contrived example.

vector<WeirdStructure>  myWeird;

/* push back a lot of stuff into the vector */ 

size_t z;
for (z = 0; z < myWeird.size(); z++)
{
    WeirdStructure& weird = myWeird[z];

    /* at this point weird is directly observable by the debugger */ 

    /* your code to manipulate weird goes here */  
}

That is the idiom I use.

Answer 3

The std::vector template guarantees the data is stored contiguously . If you take the address of the front element (say, &v[0] , for instance), you can access any other element in the vector through a C-style array. That doesn't require you to have the source code of the STL available to your debugger.

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After messing with this some, it appears that v.front() and v.begin() are likely inlined and GDB isn't finding them. I'll keep looking, but personally I would simply add the line int* i = &v[0] to the source file, and then use GDB commands on i while debugging. Note that the compiler is free to remove that dead code. You may need to output the value of i to avoid that, or simply not crank up optimizations.