How do I print the elements of a C++ vector in GDB?


Question

I want to examine the contents of a std::vector in GDB, how do I do it? Let's say it's a std::vector<int> for the sake of simplicity.

1
199
7/29/2011 8:47:59 AM

Accepted Answer

To view vector std::vector myVector contents, just type in GDB:

(gdb) print myVector

This will produce an output similar to:

$1 = std::vector of length 3, capacity 4 = {10, 20, 30}

To achieve above, you need to have gdb 7 (I tested it on gdb 7.01) and some python pretty-printer. Installation process of these is described on gdb wiki.

What is more, after installing above, this works well with Eclipse C++ debugger GUI (and any other IDE using GDB, as I think).

72
1/23/2010 1:23:51 PM

With GCC 4.1.2, to print the whole of a std::vector<int> called myVector, do the following:

print *(myVector._M_impl._M_start)@myVector.size()

To print only the first N elements, do:

print *(myVector._M_impl._M_start)@N

Explanation

This is probably heavily dependent on your compiler version, but for GCC 4.1.2, the pointer to the internal array is:

myVector._M_impl._M_start 

And the GDB command to print N elements of an array starting at pointer P is:

print P@N

Or, in a short form (for a standard .gdbinit):

p P@N

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