22_input.md

name: main

.aim[Systems: Input]

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template: main

Command Line Arguments:

• int main( int argc, char *argv[] )

  • Program name is considered the first command line argument

--

• argc
  • number of command line arguments

--

• argv
  • array of command line arguments as strings

---

template: main

Pulling data from strings

• sscanf - <stdio.h>

--

• Reads in data from a string using a format string to determine types.

--

• sscanf( char *s, char * format, void * var0, void * var1, ...)

-- - Copies the data into each variable.

-- - example int x; float f; double d; sscanf(s, ”%d %f %lf", &x, &f, &d);

template: main

stdin input

• Your OS determines the behavior of the standard input stream. Usually:
  • It captures data input via the keyboard as chracters.
  • It is a buffered file stream. This means that data will remain inside standard in until the data is read.
  • The enter key will send a newline character, but will also automatically trigger a program to read from standard in.

--

• The Standard input device (/dev/stdin) is a automatically open when a program starts at file descriptor STDIN_FILENO.

• You can use read to get input from standard in.

  • read(STDIN_FILENO, buffer, sizeof(buffer))

---

template: main

fgets

• Becasue standard in is not a normal file, and is buffered by definition, it is preferatble to use buffered operations on it, specifically fgets

• fgets - <stdio.h>
  • Read in data from a file stream and store it in a string.

--

• fgets( char * s, int n, FILE * f );
  • Reads at most n-1 characters from file stream f and stores it in s, appends NULL to the end.

-- - Stops at newline, end of file, or the byte limit.

-- - File steam - FILE * type, more complex than a file descriptor, allows for buffered input. - stdin is a FILE * variable provided when your program starts.

--

• fgets(s, 100, stdin)