Using GDB to tune the C + + standard library

I've been working on Linux all the time, but I don't have much use for gdb. Because Ping du is using qtcreator to debug the program. Because of the work, it may not be possible to rely on qtcreator again. So I have a good study ~

Before why not deep use of gdb,qtcreator to bring certain convenience is on the one hand, on the other hand, I feel that gdb encountered a vector, map, set, list there is no way to see the data.

Today I studied, in fact, is easy.

Example code:

#include <iostream> #include <string> #include <vector> #include <map>using namespace Std;int    Main () {int i1 = 32;     int i2 = 45;    Double d = i1 + I2/3;    Vector<string> Vstr;    Vstr.push_back ("Hello");    Vstr.push_back ("World");    Vstr.push_back ("!");    Map<string, int> M_si;    m_si["A"] = 12;    m_si["D"] = 93;    m_si["B"] = 77; return 0;}

Compile the time:

$ g++-O test-gdb test-gdb.cpp-g

In GDB debugging, you can use the Print command to view the values of variables or constants.

It may be that I have installed the GDB version of the higher reason, the native gdb is very supportive of the STL container. Here is the version information for my GDB:

$ gdb--versiongnu gdb (gdb) Red Hat Enterprise Linux (7.2-75.el6) Copyright (C) free software Foundation, inc.license gplv3+: GNU GPL version 3 or later 
 
The support for STL containers is excellent:
 
(GDB) P vstr$1 = std::vector of length 3, capacity 4 = {"Hello", "World", "!"} (GDB) P m_si$2 = Std::map with 3 elements = {["A"] = A, ["B"] =, ["D"] = 93}
 
It's really good to see this kind of information.
 
But my company's system of GDB is not so smart. If you print the vector, you'll get a lot of information. If it's a map, it's even scarier.
 
< here to show scary tips >
 
In fact, only a small part of the information is our concern. GDB is very flexible and we can customize the function inside. I can define a function in GDB to extract important information from the vector and display it.
 
Download a stl-views.gdb file from here. In this article, we define a lot of gdb functions such as Pvector, Pmap, pstring and so on for us to use.
 
Download this file to your home directory, and then:
 
$ cat stl-views-1.0.3.gdb >>. Gdbinit
 
This will automatically load the contents of the ~/.gdbinit file every time gdb is started.
 
13        vector<string> vstr; (GDB)  n14         vstr.push_back ("Hello");(gdb)  n15         vstr.push_back ("World");(gdb)  n16        vstr.push_ Back ("!");( GDB)  p<TAB><TAB>passcount     plist_member  print          pstring       pythonpath           pmap           print-object  ptype         pbitset        pmap_member   printf         pvector       pdequeue       ppqueue       pset          pwd            plist          pqueue        pstack         pwstring
 
After you enter P, a command that starts with P is listed each time you press the TAB key two times in a row. Here we see: pstring, Pvector, pwstring, Pstack, Pmap, Pmap_member and so on.
 
Let's use Pvector to see what's in Vstr:
 
(GDB) Pvector Vstrelem[0]: $ $ = "Hello" elem[1]: $4 = "World" elem[2]: $ = "!" Vector size = 3Vector capacity = 4Element type = Std::basic_string<char, std::char_traits<char>, std::allocator& lt;char> > *
 
This command does print out a lot of valuable information.
 
Bloggers have a habit, I want not only to know it, I also want to know why. So I took a look at the contents of the. gdbinit file. This function is defined in the ~/.gdbinit. Let's open this file and take a look.
 
define pvector    if  $ARGC  == 0         help pvector    else        set   $size  =  $arg 0._m_impl._m_finish -  $arg 0._m_impl._m_start         set  $capacity  =  $arg 0._m_impl._m_end_of_storage -  $arg 0._m_ impl._m_start        set  $size _max =  $size  -  1    end    if  $ARGC  == 1         set  $i  = 0        while  $i   <  $size             printf  "elem[%u]:   ",  $i             p * ($arg 0._m_impl ._m_start + $i)             set  $i ++         end    end    if  $ARGC  ==  2        set  $idx  =  $arg 1         if  $idx  < 0 | |   $IDX  >  $size _max             printf  "idx1, idx2 are not in acceptable range: [0..%u].\n",  $ size_max        else             printf  "elem[%u]: ",  $idx              p * ($arg 0._m_impl._m_start +  $idx)          end    end    if $argc == 3      set  $start _idx =  $arg 1       set  $stop _idx =  $arg 2      if  $start _idx  >  $stop _idx        set  $tmp _idx =  $start _ idx        set  $start _idx =  $stop _idx         set  $stop _idx =  $tmp _idx      end       if  $start _idx < 0 | |   $stop _idx < 0 | |   $start _idx >  $size _max | |   $stop _idx >  $size _max        printf  "idx1,  idx2 are not in acceptable range: [0..%u].\n ",  $size _max       else        set  $i  =  $start _idx        while  $i  < =  $stop _idx            printf  "elem[%u]:   ",  $i             p * ($arg 0._m_impl ._m_start +  $i)             set  $i + +         end      end     end    if  $ARGC  > 0         printf  "vector size = %u\n",  $size          printf  "vector capacity = %u\n",  $capacity          printf  "element "         whatis  $arg 0._m_ Impl._m_start    endenddocument pvector    prints std::vector<t>  Information.    syntax: pvector <vector> <idx1> <idx2 >    Note: idx, idx1 and idx2 must be in  Acceptable range [0..<vector>.size () -1].    examples:     pvector v - prints vector content, size, capacity and t  typedef    pvector v 0 - prints element[idx] from  vector    pvector v 1 2 - prints elements in  range [idx1. Idx2] from vectorend
 
 Look at all a bit more, we don't look at the part of multiple parameters, we analyze only one part of the parameter: 
 
 
define pvector    if  $ARGC  == 0            #  If there are no parameters, print the Help tip information         help  pvector    else                     #  If there are parameters, then prepare the Size, capacity, size_max   These three important parameters.         set  $size  =  $arg 0._m_impl._m_finish -   $arg 0._m_impl._m_start        # arg0  is the first parameter, That is, the Vstr array object. Pay attention to how  size  is calculated.         set  $capacity  =  $arg 0._m_impl._m_end_of_storage  -  $arg 0._m_impl._m_start        set  $size _max =   $size  - 1    end    if  $ARGC &NBsp;== 1           #  If there is only one parameter, Description requires printing out all elements of the vector         set  $i  = 0                   while  $i   <  $size     #  with a  while  loop, print out all the elements in the list with printf and P              printf  "elem[%u]: ",  $i              p * ($arg 0._m_impl._m_start +  $i)       #  Watch!!!!             set  $i ++         end    end
 
All the instructions are written in the comments above, you have to realize it!
 
If the print command can be like a template function in C + +, it can be "biased" for a particular type. There is a problem with the above:
 
In the "P * ($arg 0._m_impl._m_start + $i)" command, what if a member of the vector is still a STL container? It's a question.
Using GDB to tune the C + + standard library