c++: GDB & G++ compiler
G++
Best thing to do for g++ is consult the manual $man g++
| Flags | |
|---|---|
-Wall |
will print out all warnings |
-g |
enables debugging |
-ftime-report |
Nice little report at the end - very useful when testing the time and space results of the GCC passes and phases |
| -fmem-report | Makes the compiler print some statistics about permanent memory allocation when it finishes. |
| -time | Report the CPU time taken by each subprocess in the compilation sequence. For C source files, this is the compiler proper and assembler (plus the linker if linking is done). |
-l |
lets the compiler know what other libraries to use |
-I |
guides the compiler to the folder where it can find the include files |
-o |
sets the output of the process |
-O 0 |
Turns off the optimisation - useful when debugging |
-E |
do the Pre-Processing operation - this will just output it to the terminal if you want to catch the output you either do a > in the terminal or set a -o flag. |
-S |
takes the Pre-compiled file and transforms into Assembly - many times I find it quite interesting to read what the assembly code is doing in specific instances. It’s worth noting that this can also be read by using the gdb. |
-S -masm=intel |
outputs the code in intel syntax |
-c |
takes whatever you feed to it - pre-compiles and transforms it into assembly if needed. Then puts the Assembler to work into transforming the Assembly code into binary the default extension is .o and the files are called objects. This is what the machine actually reads. The |
` $g++ | just worth mentinoning that when you call g++` the linker will link every file that is in its input. |
|
| -v | Verbose mode. Print out GNU CPP ‘s version number at the beginning of execution, and report the final form of the include path. |
| -H | Print the name of each header file used, in addition to other normal activities. Each name is indented to show how deep in the #include stack it is. Precompiled header files are also printed, even if they are found to be invalid; an invalid precompiled header file is printed with …x and a valid one with …! . |
| Libraries | these libraries can be found at the path: /usr/include/GL/ this is the default path that G++ will use in finding the libraries that are called with -l |
|---|---|
-lGL |
OpenGL library |
-lGLEW |
GLEW library |
-lSDL2 |
LSDL 2 library |
It is worth saying that the terminal reads g++ from /usr/bin and this can be tested with running which g++.
GDB
I have been coding quite a bit lately for #leetcode30daychallenge and I choose mostly to do it in C++.
I truly enjoy C++ and am enjoying both refreshing and learning new concepts about it. Let’s jump in
GDB oftenly used commands
| Name | Command | What it does |
|---|---|---|
| TUI (Text User Interface) | ctrl+x+a |
it opens the Text User Interface of the GDB. the same thing as layot next or layout src. |
| layout next | layout next |
Iterates to the next view layout |
| List | l or list |
- prints out the source code centred around the line we are currently at |
| list + number line | l 13 |
will print out the code centred around line 13 |
| Next | n or next |
executes the next line of code |
| step | s or step |
steps into the next line of code (for functions) |
| print + variable name | p or print a |
prints the content of a variable |
p a = 2 |
by using p and specifying the value of a variable, you can set the variable to a specific amount from GDB | |
| set var | set var x = 2 |
Sets a specific variable to a specific value |
| info locals | info locals |
Prints out all the local variables |
| breakpoint | b or break |
it’s good practice to set the file when using this, just to avoid confusion with multi file projects. for example b test.cpp:13 |
| disable break points | disable |
disables all the breakpoints |
| continue | c or continue |
Continues to the next breakpoint or to the end of the file |
| registers | info reg |
Displays the registers |
Breaks
You can add conditional breaks like b if (i==4) and the program will break
when i==4.
-x flag
You can write a separate file containing all the commands to be executed within gdb. This can be loaded with the -x flag.
# a.db
b 3
b 24
define sumA
print $arg1 + $arg2 + $arg3
end
This will put a break point at location 3 and 24 and define the function sumA that returns the sum of 3 arguments. In gdb the sum can be called
(gdb) sumA 1 2 3