CSE2031 Lecture 1

Course Information

Prof: Gordon Turpin

Email: gordon@cse.yorku.ca

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    -use a subject header "2031: …"

 

Hello World

 

#include <stdio.h>

int main(void)

{

printf("Hello World!"\n");

return 0;

}

• #include <stdio.h>
  
  • This file is replaced in the header in compile time
    
  • stdio.h does not contain executable code
    
    • only definition of constants
      
    • include statements
      
    • and function prototypes
      
    • 'printf'
      
      • A function call
        
      • (method is a function, method is a java term)
        
      • When it encounters a function call like 'printf'
        
        • It wants the function prototype of printf
          
• int main(void)
  
  • 'void' means it takes no parameters
    
  • 'main' returns an 'int'
    
• return 0;
  
  • indicates success
    
  • unspecified types are assumed to be 'int'
    
• printf
  
  • most basic print type
    
  • '\n' sends a new line after the text
    
• This program doesn't return a '0' because printing is not the same as returning
  

 

Compiling C

• Simplest way to compile
  

  cc hello.c
  

  ls a.out
  

  cat hello.c
  

• 'cat' prints out the code for hello.c in console
  
• cat is called from /bin/cat
  
• cc is the compile command
  
  • cc created a.out
    
    • to create a different file name
      
      • use cc –o hello hello.c
        
        • 'hello' is the filename
          
        • -o is the 'flag' to create a different name
          
      • cc –o hello –Wall hello.c
        
        • –Wall will allow the compiler point out errors in code
          
      • cc –o hello –Wall -pedantic hello.c
        
        • allows you to see if code will run on older versions of C
          
      • cc –o hello –Wall -pedantic –c hello.c
        
        • stops compilation when the object module is produced
          
        • Produces the file 'hello.o'
          
        • nm hello.o
          
          • shows the function 'main' in the T (text)
            
          • and there is a call for a function 'printf'
            
      • cc –o hello –Wall –pedantic –c -E hello.c
        
        • stops the compilation after the preprocessor phase
          
        • Replaces #define with code supplied for that function
          

          
           

• echo $PATH
  
  • returns the paths where the shell will look for the commands you are passing
    
    • separated by ':'
      
  • the last place bash looks in is the current directory
    
  • ./a.out will find a.out within your path
    
  • PATH=$PATH:..
    
    • Adds ' ..' to the $PATH
      
• a.out only needs executable permission to run
  
• if you write a shell script you would need execute and read permission
  

 

chmod

• 9 permission bits
  
  • ---------
    
    • User
      
  • ---------
    
    • Group
      
  • ---------
    
    • Owner    
      
  • Read = 4
    
  • Write = 2
    
  • Execute = 1
    
  • Non = 0
    
• 'chmod 751 a.out 'gives
  
  • user
    
    • r/w/e
      
  • group
    
    • r/e
      
  • owner
    
    • e
      

Comments

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