using gdb to see into a c++ vector?

[jinxjinx]

i have a vector of floats, is there anyway to use gdb to see whats inside?

Thanks

[Calculator]

Perhaps this is of interest.

http://staff.science.uva.nl/~gilad/stl/stl_gdb.html

[jinxjinx]

well, that sucks....
thanks for the reply

[Calculator]

Supposedly you can just evaluate expressions and print it, but it doesn't work for me.

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This GDB was configured as "i686-pc-mingw32"...
(gdb) break *0x004013ef
Breakpoint 1 at 0x4013ef: file t.cpp, line 9.
(gdb) run
Starting program: a.exe

Breakpoint 1, 0x004013ef in main (argc=1, argv=0x3d3cd8) at t.cpp:9
9               v.push_back(3);
(gdb) p v[0]
One of the arguments you tried to pass to operator[] could not be converted to w
hat the function wants.
(gdb)

[treuss]

You have to know how the vector is implemented. If you are using the same gcc version I use, vector is a struct that contains an element _M_start which points to the first member.

(gdb) r
Starting program: /home/treuss/src/vec2

Breakpoint 1, main () at vec2.cc:5
5         std::vector<float> v;
(gdb) n
6         v.push_back( 3.14 );
(gdb) n
7         v.push_back( 2.63 );
(gdb) n
8         exit( 1 );
(gdb) p *v._M_start
$1 = 3.1400001
(gdb) p *(v._M_start+1)
$2 = 2.63000011

Hope this helps.

[Paul McKenzie]

As treusss mentioned, if you know how to get a pointer to the vector's internal buffer, then it's just a matter of going to the n'th element starting at the pointer to the buffer. Since a vector stores its values in contiguous memory, it is much simpler to view a vector's values then say, a std::list or std::map.

Overloaded operators are not supported by most debuggers, which is why using v[0] didn't work. To see v[0], you must call a function to invoke [], and most debuggers do not support function calling.

Regards,

Paul McKenzie

[wingdb]

This topic is quite old, but problem is still present. If somebody would like to run gdb under VisualStudio, then please check our addin WinGDB. Browsing of vectors will be much easier, than directly under gdb

Kind regards,
WinGDB team