Continuing and SteppingUp:
You use this number to refer to that breakpoint.
To see the list of all breakpoints and watchpoints you've set, type info breakpoints which can be abbreviated by i b. I show a sample resulting output: They are assigned to numbers 1 and 2 respectively. There is also a watchpoint set: In addition to being assigned a number, each breakpoint and watchpoint can be enabled or disabled.
A program's execution won't stop at a disabled breakpoint or watchpoint. By default, when you create a new breakpoint or watchpoint, it's enabled. To disable the breakpoint or watchpoint assigned to number n, type: Compile and run the fgets program, which is a multi-filed program the files are fgets.
That's because we used -W -Wall which instructs gcc to tell us when it sees what it thinks might be a common programming error. The best way to debug your program is to not put the bugs in the program to begin with.
You should always use these gcc bug finding options. Let me be blunt here, and I hope I don't offend anyone. It's stupid not to use -W -Wall when you compile code. With a capital S. Most people don't use them, even people who are clearly better programmers than me. That's because even smart people can do dumb things.
Don't you be dumb. Always use -W -Wall. The program is a password guessing program. Take a moment to look through the code to see how it works.
The program is ultra-simple so we can focus on learning GDB rather than trying to figure out complicated code like linked lists and whatnot.
You should be able to deduce how the program works and what the password is in under a few seconds.
Now run the code and notice it simply doesn't work. We'll first concentrate on learning how to set breakpoints, and then we'll debug the program. There are four major ways to set a breakpoint, in roughly the order that I personally use them.: By filename and line number.
By Function Name We've already seen the most common way of setting a brekpoint: If we now run the program, the program will stop at line 6. Recall from the previous discussion that this means that GDB will be sitting between lines 5 and 6.
Line 6 will not have executed until we issue the step command: The line number refers to the file GDB is currently in.
Right now, we're in main. Let's set a breakpoint at line 9, where the printf statement is.
Once GDB pauses due to a breakpoint, the continue command will resume execution. Use continue to make sure that GDB pauses at line 9: Breakpoint 2, main at main. Let's see if you can guess it.Breakpoints, Watchpoints, and Catchpoints. to specify the place where your program should stop by line number, function name or exact address in the program.
You can arrange to have values from your program displayed automatically whenever GDB stops at a breakpoint. Debugging Programs with GDB. This is a description of several of the gdb features that are useful for debugging your programs. The gdb session shown below was generated while debugging the program benjaminpohle.com Must compile and link with -g option >g++ -g -o gdbprog benjaminpohle.com GDB assigns a number to each breakpoint, watchpoint, or catchpoint when you create it; these numbers are successive integers starting with one.
In many of the commands for controlling various features of breakpoints you use the breakpoint number to say which breakpoint you want to change. GDB has a console GUI option available with the command line option --tui. Text console User Interface: gdb --tui Command just like regular GDB with a source screen showing source code and break points.
My favorite gdb GUI is ddd. Awesome variable and memory interrogation. One application for breakpoint commands is to compensate for one bug so you can test for another.
Put a breakpoint just after the erroneous line of code, give it a condition to detect the case in which something erroneous has been done, and give it commands to assign correct values to . For some targets, gdb can automatically decide if hardware or software breakpoints should be used, depending on whether the breakpoint address is read-only or read-write.
This applies to breakpoints set with the break command as well as to internal breakpoints set by commands like next and finish.