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Useful G++ and GDB Flags and Commands

  • g++ -g: includes extra debuggin information
  • gdb ./a.out: this takes one argument, which is the file to run
  • gdb -q: run quietly
  • gdb -x: run gdb commands from file
  • gdb file/exec-file: specify the file to run
  • gdb run: run file with debugger with the current set arguments by run or by set args
  • gdb show args: show the current set arguments
  • gdb break +offset & break -offset: set a breakpoint some number of lines forward or back from the position at which execution stopped in the currently selected stack frame.
  • gdb start: instruct the debugger to start and breaks the program before the execution of the main() body
  • gdb starti: instruct the debugger to start and directly break the execution of the program before the first instruction
  • gdb stepi: instruct the debugger to step into next instruction
  • gdb nexti: instruct the debugger to step over next instruction, in other words, doesn't get into functions
  • gdb continue: continues execution of program normally
  • gdb finish: instruct the debugger to step out of current function
  • gdb info proc mappings: report memory address space ranges
  • gdb frame: reports the current line with the line number
  • gdb frame 1: reports the calling line with the line number
  • gdb info locals: All local variables of current stack frame or those matching REGEXPs
  • gdb print: prints the contents of a variable
  • gdb output: like print but doesn't print $# = and a newline
  • gdb *: can be used in an expression to dereference a pointer
  • gdb (new type): casting works in gdb expressions too
  • gdb break operator new: creates a break point at every use of operator new
  • gdb ptype: print type
  • gdb dump memory heap_1.bin 0xheap_start_address 0xheap_end_address: dump the heap
  • gdb macro define offsetof(t, f) (size_t)&((t *) 0)->f: defines the offset macro that can then be used as follows p offset(t, f) where t is the class f is the variable and the byte offset is returned
  • gdb x/16bx address: inspect 16 bytes in hexadecimal starting from address
  • gdb p sizeof(My_class): print the size of an object of class My_class
  • gdb watch var: creates a watchpoint on the variable, in other words, execution will break if the variable's value changed
  • bash command 2> error 1> output: redirects error and output to error and output respectively
  • gdb print &((Node *)(0x55555556b2c0)).next
  • gdb set logging file <file>: sets the logging file, the file to redirect gdb output to
  • gdb set logging overwrite [on|off]: sets whether to overwrite the logging file or append to it
  • gdb set logging redirect [on|off]: sets whether to redirect and not even print the output to the screen or do both
  • gdb set logging [on|off]: turns logging on or off