Computer Programming 1 Lab

2020-12-31

Outline

  • Command line argument
  • Stream
  • Redirect
  • Pipe
  • File

Command line argument

  • Pass argument to main function from command line
  • args: the number of command line argument
  • argv: an array of strings in which the actual command-line arguments are stored.
./a.out data1.in data2.in data3.in
->
args: 4
argv[0] = ./a.out
argv[1] = data1.in  
argv[2] = data2.in 
argv[3] = data3.in

Stream

A “source” or “sink” of data.

Common streams:

  • FILE I/O
  • Socket
  • STDIN/STDOUT/STDERR
FILE* file_1 = fopen(.......); 
FILE* file_2 = fopen(.......); 

fgets(str, sizeof(str), stdin);
fgets(str, sizeof(str), file_1); 

fputs(str, stdout); 
fputs(str, file_2); 

fprintf(stdout, ......); 
fprintf(stderr, ......);

Redirect

myprogram > output.txt 
myprogram 2> err.txt 
myprogram > output.txt 2> err.txt

Pipeline

  • |

  • Simply, '|'

  • Connecting multiple program procedures' stdout and stdin like a waterfall, like ONE stream.

  • Program_A:
    Prints 1 ~ 10 ascendingly
  • Program_B:
    Reads a number and multiply it by 2

Than prints the result
Program_A | Program_B

Any Question?