Linux/C + + GDB tutorials Detailed __linux

A very useful article on the web, it is worth in Linux C + + developers to view.

After learning to use GDB for a while, find it really good and powerful. Good.

GDB is a powerful UNIX program debugging tool released by the GNU Open source organization. Perhaps, you like the graphical interface, such as VC, BCB debugging IDE, but if you are in the UNIX platform to do the software, you will find that the debugging tool GDB is more than VC, BCB graphics debugger more powerful features. The so-called "inch, the ruler has short" is this truth.

In general, GDB mainly helps you complete the following four aspects of the function:

1, start your program, you can follow your custom requirements of the arbitrary operation of the program.
2. You can let the program being debugged stop at the breakpoint where you specify the adjustment. (A breakpoint can be a conditional expression)
3. When the program is stopped, you can check what happens in your program at this time.
4, dynamic changes in the execution of your program environment.

From the above, GDB is no different from the usual debugging tools, basically complete these functions, but in detail, you will find GDB this debugging tool is powerful, you may be more accustomed to the graphical debugging tools, but sometimes, the command line debugging tools are not completed by the graphical tools. Let's see it all.

A debugging example
——————

SOURCE program: TST.C

1 #include <stdio.h>
2
3 int func (int n)
4 {
5 int sum=0,i;
6 for (i=0; i<n; i++)
7 {
8 sum+=i;
9}
return sum;
11}
12
13
Main ()
15 {
int i;
Long result = 0;
for (I=1; i<=100; i++)
19 {
result = i;
21}
22
printf ("result[1-100] =%d/n", result);
printf ("result[1-250] =%d/n", func (250));
25}

Compile Build Execution file: (under Linux)
hchen/test> cc-g Tst.c-o TST

Debugging with GDB:

hchen/test> gdb TST <----------start GDB
GNU gdb 5.1.1
Copyright 2002 Free Software Foundation, Inc.
The GDB is free software, covered by the GNU general public License, and your are
Welcome to change it and/or distribute copies of it under certain conditions.
Type ' show copying ' to the conditions.
There is absolutely no warranty for GDB. Type ' show warranty ' for details.
This is GDB was configured as "I386-suse-linux" ...
(GDB) L <--------------------l command is equivalent to the list, starting with the first line of the original code.
1 #include <stdio.h>
2
3 int func (int n)
4 {
5 int sum=0,i;
6 for (i=0; i<n; i++)
7 {
8 sum+=i;
9}
return sum;
(GDB) <--------------------Direct carriage return, repeat the last command
11}
12
13
Main ()
15 {
int i;
Long result = 0;
for (I=1; i<=100; i++)
19 {
result = i;
(GDB) Break <--------------------set breakpoints at the 16th line of the source program.
Breakpoint 1 at 0x8048496:file tst.c, line 16.
(GDB) Break Func <--------------------set a breakpoint at the func () entrance of the function.
Breakpoint 2 at 0x8048456:file tst.c, line 5.
(GDB) Info Break <--------------------view breakpoint information.
Num Type Disp ENB address What
1 breakpoint Keep Y 0x08048496 in main at tst.c:16
2 Breakpoint Keep Y 0x08048456 in func at Tst.c:5
(GDB) R <---------------------running programs, Run command shorthand
Starting program:/HOME/HCHEN/TEST/TST

Breakpoint 1, Main () at Tst.c:17 <----------stop at the breakpoint.
Long result = 0;
(GDB) n <---------------------A single statement is executed, and the next command is abbreviated.
for (I=1; i<=100; i++)
(GDB) n
result = i;
(GDB) n
for (I=1; i<=100; i++)
(GDB) n
result = i;
(GDB) C <---------------------continue to run the program, continue command shorthand.
Continuing.
RESULT[1-100] = 5050 <----------program output.

Breakpoint 2, func (n=250) at Tst.c:5
5 int sum=0,i;
(GDB) n
6 for (i=1; i<=n; i++)
(GDB) P i <---------------------the value of the print variable i and the Print command is abbreviated.
$ = 134513808
(GDB) n
8 sum+=i;
(GDB) n
6 for (i=1; i<=n; i++)
(GDB) P sum
$ = 1
(GDB) n
8 sum+=i;
(GDB) P I
$ = 2
(GDB) n
6 for (i=1; i<=n; i++)
(GDB) P sum
$ = 3
(GDB)BT<---------------------view the function stack.
#0 func (n=250) at Tst.c:5
#1 0x080484e4 in Main () tst.c:24
#2 0x400409ed in __libc_start_main () from/lib/libc.so.6
(GDB)Finish<---------------------Exit Function.
Run till exit from #0 func (n=250) at Tst.c:5
0x080484e4 in Main () at tst.c:24
printf ("result[1-250] =%d/n", func (250));
Value returned is $ = 31375
(GDB) C <---------------------continue to run.
Continuing.
RESULT[1-250] = 31375 <----------program output.

Program exited with code 027. <--------program exits and debugging ends.
(GDB) Q <---------------------exit gdb.
Hchen/test>

Well, with the above perceptual knowledge, or let us have a systematic understanding of GDB bar.

Use GDB
————

In general, GDB is primarily debugging C + + programs. To debug a C + + program, first at compile time, we have to add debug information to the executable file. You can do this with the-g parameter of the compiler (cc/gcc/g++). Such as:

> cc-g hello.c-o Hello
> g++-G hello.cpp-o Hello

Without-G, you will not see the program's function name, variable name, instead of all the run-time memory address. When you add the debug information with-G and successfully compile the target code, let's see how to debug it with GDB.

There are several ways to start gdb:

1, GDB <program>
Program is your executable file, usually in the course of the directory.

2. GDB <program> Core
Using GDB to debug both a running program and a core file, the core is the file that was generated after the program was illegally executed after the core dump.

3, GDB <program> <PID>
If your program is a service program, then you can specify the process ID of the service program at run time. GDB will automatically attach up and debug him. program should be searched for in the PATH environment variable.

When GDB starts, you can add some gdb startup switches, and the detailed switches can be viewed with gdb-help. I'll just cite some of the more commonly used parameters below:

-symbols <file>
-S <file>
Reads the symbol table from the specified file.

-se file
Reads the symbol table information from the specified file and uses it in the executable file.

-core <file>
-C <file>
Core dump core file when debugging.

-directory <directory>
-D <directory>
Add a search path to a source file. The default search path is the path defined by path in the environment variable.

Overview of GDB's commands
———————

After you start GDB, you are brought into the GDB debugging environment, you can use the GDB command to start the debugger, GDB commands can use the Help command to view, as follows:

/home/hchen> GDB
GNU gdb 5.1.1
Copyright 2002 Free Software Foundation, Inc.
The GDB is free software, covered by the GNU general public License, and your are
Welcome to change it and/or distribute copies of it under certain conditions.
Type ' show copying ' to the conditions.
There is absolutely no warranty for GDB. Type ' show warranty ' for details.
This is GDB was configured as "I386-suse-linux".
(GDB) Help
List of classes of commands:

    Aliases--aliases of other commands
    breakpoints--making program stop at CE Rtain points
    data--examining data
    files--Specifying and examining files< br>     Internals--Maintenance commands
    obscure--obscure features
 &nb sp;  running--running the program
    Stack--examining the stack
    status --Status Inquiries
    Support--support facilities
    tracepoints--tracing of Program execution without stopping
    user-defined--user-defined commands

Type ' help ' followed by the A class name for a list of the commands in that class.
Type ' help ' followed by the command name for the full documentation.
Command name abbreviations are allowed if unambiguous.
(GDB)

GDB has a lot of commands, and gdb divides it into many categories. The help command is just an example of the GDB command type, and if you want to see the commands in the category, you can use the helps <class> command, such as the breakpoints, to see all the commands that set breakpoints. You can also help <command> directly to view the commands.

GDB, when you enter a command, you do not have to call full command, only the first few characters on the command can be, of course, the first few characters of the command should mark a unique command, in Linux, you can hit two times tab to get the full name of the command, if there are duplicates, then GDB will take it out.

Example one: When entering function func, set a breakpoint. can be typed break func, or directly is B func
(GDB) b func
Breakpoint 1 at 0x8048458:file hello.c, line 10.

Example two: typing B press two times tab, you will see all the B-Start command:
(GDB) b
BackTrace Break BT
(GDB)

    Example Three: Only remember the prefix of the function, you can do this:
    (gdb) b make_ < Press the TAB key
    (Press the TAB key again and you will see:)
    make_a_section_from_file     Make_environ
     make_abs_section             Make_ Function_type
    make_blockvector              Make_pointer_type
    make_cleanup                  Make_reference_type
    make_ command                 Make_ Symbol_completion_list
    (gdb) b make_
    gdb gives you all the functions that start with make. See