Elijah's Notes

C and GDB Review

1 min read

Purpose

Capture the small set of C and GDB ideas that came up in section. This is a compact memory aid, not a full language reference.

C Review

static: has different meanings

  • static functions cannot be used outside the file where they are defined
  • static local variables keep one storage location across function calls

extern: declares variable without allocating any memory for it

  • variables must be defined somewhere else
  • allows you to use variables from other files
 
void change(char** s) { *s = "class"; }
 
int main() {
   char* s = "hello";
   char* w = s;
 
   change(&w);
}

When you use an uninitialized pointer, the address that the pointer stores is the uninitialized part, and will probably lead to errors when it is interpreted as an address.

GDB Review

printf debugging is useful, but limited once the program state changes quickly or multiple threads are involved.

Enter gdb.

run <...args>: start execution

n: next instruction

bt: backtrace

watch <variable>: breakpoint when it changes

p <opt> <arg>: print arg

x <opt> <arg>: examine memory at an address

Graph View