CMSC212: Intro to Low-Level Programming Concepts

CMSC212: Intro to Low-Level Programming Concepts Section 0101: 9:00am – 9:50am Section 0102: 10:00am-10:50am Monday & Wednesdays Room 3118

Emacs Stuff • With Xming • [emacs &] calls up a new window with emacs and returns access to command-line • [emacs file1 &] calls up emacs with file1 read into new window • Note: & commonly used to put process into background • [bg] to view background processes • [fg %number] to pull background process “number” to foreground

Emacs Stuff Cont’d • Without Xming • [emacs], [emacs file1] • More commands • [Ctrl-x Ctrl-c] Exit emacs • [Ctrl-x Ctrl-s] Save file (save often) • Useful keybinds for cursor movement • [Ctrl-a] Beginning of current line • [Ctrl-e] End of current line • [Escape-<] Front of file • [Escape->] End of file

Emacs Editing • Keybinds for deleting text • [Ctrl-k] Delete to end of line • [Ctrl-u] Delete line • Cut/pasting • [Ctrl-space] Mark head end of cut • [Ctrl-w] Mark tail end of cut • [Ctrl-y] Paste

GCC Compilation and Linking • File test1.c • #include <stdio.h>int main() { printf("This is CMSC 212."); printf(“hello world!\n"); printf(“bye world!\n"); return 0; }

GCC Compilation and Linking • Method 1 • [gcc –c test1.c] • Creates an object file test1.o • [gcc test1.o –o test1] • Links object file(s) and outputs executable • Method 2 • [gcc test1.c] • No intermediates, produces executable a.out • [gcc test1.c –o test1] • No intermediates, produces executable test1

Gcc Compilation and Linking Multiple files • File1: questionablepractices.h • #ifndef _QUESTIONABLE_H_#define _QUESTIONABLE_H_#include <stdio.h> //Prototypesvoid infiniteLoop();void infiniteStack();#endif

Gcc Compilation and Linking Multiple files • File2: questionablecode.c • #include “questionablepractices.h”void infiniteLoop(){ while(1) printf(“how to terminate?\n”);} void infiniteStack(){ printf(“o really?\n”); infiniteStack();}

Gcc Compilation and Linking Multiple files • File3: questionablemain.c • #include “questionablepractices.h”int main(){ infiniteLoop(); //infiniteStack(); return 0;}

Gcc Compilation and Linking Multiple files • How to build this? • gcc questionablemain.c questionablecode.c -o question • Generates executable called “question” • gcc –c questionablemain.c questionablecode.c • Generates object files questionablemain.o questionablecode.o • gcc questionablemain.o questionablecode.o -question • Links the two files and creates executable

Xming emacs + compilation • Another way to compile directly through emacs • [Escape-x] type compile • Suggests make –k (will get into later when we use make) • For now, use the standard gcc commands • Notice the new menu titled “Compile”

More Unix commands+options • More useful commands • [cp –r] Copy directories recursively, i.e. all sub-file/directories • [man cmd] pulls up the manual and description of options for cmd, e.g. [man cp]

Chmod • [chmod [references][operator][mode] file(s)] • reference classes • u (user/owner), g (users who are members of file group), o (users not in g), a (all from before, i.e. ugo) • operator • + (add modes to reference classes) • - (remove modes from reference classes) • = (specified modes are made exact for reference classes) • Mode • r (read), w (write), x(execute) • X, s, t (not covered)

Chmod • E.g. • chmod ug+rw mydir • Gives read/write mode to user and file group of directory mydir

Questions?

CMSC212: Intro to Low-Level Programming Concepts