course-c

History

• Originally designed and implemented by Dennis Ritchie on a DEC PDP-11

• Influenced by B written by Ken Thompson in 1970

• First C standard in 1988 by ANSI (C89)

• Adopted by ISO in 1990 (C90)

• Most recent standard C99 by ISO

• Compiled language

• Source code portable

C program – hello.c

#include <stdio.h>

 /* function main - print hello world */
int
main()
{
    printf("hello world!\n");
    return 0;
}

C program structure

• Multi-line comments begin with /* and end with */, these are called delimiters

• # is used to begin pre-processor directives

• Execution of a C program begins at function main
  • main can return an int value to the operating system otherwise it should return void

• Code blocks and function bodies begin with { and end with }

• C statements end with a semicolon ;

Executing hello.c

• Use GCC

  gcc hello.c -o hello -Wall
  

• Without -o option the output is named a.out

• Execute

  ./hello
  

• Output

  hello world!
  

Compilation process

• Compiler produces the executable by performing the following steps

  • Pre-processing

  • Compilation and assembly

  • Linking

Pre-processing

• Conceptual first step in compilation

• Two tasks commonly performed

• File inclusion with #include directive

  #include <stdio.h>
  

• Macro substitution with #define directive

  #define pf printf
  pf("hello world!")
  

Compilation and assembly

• Lexical and semantic analysis to generate intermediate code

• Transform the intermediate code to assembly or machine code

• Creating an object file using GCC

  gcc hello.c -c
  

  • The -c option tells GCC not to perform linking

  • A file called hello.o is produced

Linking

• Linking combines all the object files and required library code to produce a single executable

  gcc hello.o -o hello
  

Multiple source files – hello.c

#include "print.h"
/* Function main - Print hello world */
int
main()
{
  print_hello();
}

Multiple source files – print.c

#include <stdio.h>
#include "print.h"
void print_hello()
{
  printf("printing: hello world!\n");
}

Multiple source files – print.h

#ifndef _PRINT_H_
#define _PRINT_H_

extern void print_hello();

#endif //_PRINT_H_

• #ifndef / #endif prevents pre-processor from including same file twice

Simple compilation

• Compile and link using gcc

  gcc hello.c print.c -o hello
  

• Execute

  ./hello
  

• Output

  printing: hello world!
  

Complex Compilation - With Error

• Compile hello.c using gcc; produces hello.c

  gcc hello.c -c
  

• Compile print.c; produces print.o

  gcc print.c -c
  

• Link using gcc

  gcc hello.o -o hello
  

  hello.o(.text+0x27):hello.c: undefined reference to `_print_hello'
  collect2: ld returned 1 exit status
  

Complex Compilation – Correcting the Error

• Link using gcc

  gcc hello.o print.o -o hello
  

• Using ld

  ld -o hello \
  /lib/crt0.o -L/opt/gcc.3.3/lib/gcc-lib/i586-pc-interix3/3.3 \
  hello.o print.o -lgcc -lc -lpsxdll -v
  

  • Calling gcc with -v switch shows how
  • Note path to libgcc.a in my Windows SFU installation

Using a Graphical Debugger

• DDD is a graphical debugger for X Windows and it uses gdb, the command line debugger

• Re-compile source code with extra debug information for gdb

  gcc -g hello.c print.c -o hello
  

• Execute ddd

  ddd hello
  

• Try stepping through code and adding watch expressions

• Repeat with VS Code

Debug Using DDD

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Debug Using VS Code

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Other Topics

• Creating static and shared libraries

• Dynamic linking

• GCC compile, link and optimize options

• Building applications with make

• Using an IDE for C/C++ development