1. C Preprocessing File I/O

2. C Preprocessor Modifies C code "to save typing" Define constants
Define macros
Include files
Other parameters (time of compilation...)

3. Preprocessor constants
Define a symbolic constant like so
#define PI
Better version
#define PI ( )
Use the symbolic constant
circle_length = 2 * PI * radius ;

4. Preprocessor constants (2)
Check if constant defined ( #ifdef )
#define VERBOSE
. . .
#ifdef VERBOSE
printf("I am extremely glad to see you !\n");
#else
printf("Hi !\n");
#endif

5. Preprocessor Macros Parameterized Macros:
Similar to function calls. Symbolic parameters !
#define SQUARE( x ) x * x
Better version:
#define SQUARE( x ) ((x) * (x))
Usage:What will be the output for each version?
int x
x = SQUARE ( );
 (1+2+3*1+2+3) =???
printf( " x = %d \n", x ); is x=11?, or is it, x=36?
How do you fix it to generate 36?  ((1+2+3) * (1+2+3))

6. Including files Used to include header files
Can be used to include any file
Beware of including header files twice
#include "MyFileName.c"

7. Header files
Usually define function prototypes, user defined types and global variables.
Avoid including twice
int x; /* included from myHeader.h */
Standard header file header
#ifndef MyHeaderFile_H
#define MyHeaderFile_H
/* header file contents goes here */
#endif

8. See this Example /* example.c */ #include <stdio.h>
#define ONE 1
main(){
if(ONE != 1)
return 0;
printf("The answer is %d.\n", myfunc(2,6) ); }
myfunc( int a, int b) {
int i = ONE, j = ONE;
for( ; i <= b; ++i) j = j * a;
return j;
See this Example

9. File Input / Output

10. What is a File A file is a collection of related data
"C" treats files as a series of bytes
Basic library routines for file I/O
#include <stdio.h>

11. Basics About Files Files must be opened and closed
#include <stdio.h>
. . .
FILE * myFile;
myFile = fopen ("C:\\data\\myfile.txt", "r"); // Name, Mode (r: read)
if ( myFile == NULL ){ // (w: write)
/* Could not open the file */
... }
fclose ( myFile );
Note: status = fclose(file-variable)
status = 0 if file closed successfully- Error otherwise.

12. End-line Character
Teletype Model 33 (long time ago...) used 2 characters at the end of line.
RETURN character
LINE FEED character
Computer age
UNIX: LINE FEED at the end of line: "\n"
MS-DOS/Windows: both characters: "\n\r"
Apple: RETURN at the end of line: "\r"

13. File Types Text (ASCII) files Binary files Special (device) files
stdin - standard input (open for reading)
stdout - standard output (open for writing)
stderr - standard error (open for writing)

14. Operations with Files Writing (w) Reading (r) fopen() revisited
sequential
random
appending (a)
Reading (r)
sequential
random
fopen() revisited
FILE *fOut;
fOut = fopen("c:\\data\\log.txt", "w" );

15. Useful File I/O Functions
fopen(), fclose() open/close files
fprintf ( myFile, "format...", ...) -- formatted I/O
fscanf ( myFile, "format...", ...)
fgets(), fputs() for line I/O
fgetc(), fputc() for character I/O
feof() -- end of file detection, when reading

16. Binary and Random I/O Binary I/O Positioning for random I/O
readSize = fread(dataPtr, 1, size, myFile);
//size of data read, if < size then encountered an error.
writeSize = fwrite(dataPtr, 1, size, myFile);
Positioning for random I/O
fseek(myFile, 0, SEEK_SET);
fseek(myFile, 10, SEEK_CUR);
fseek(myFile, 0, SEEK_END);

17. Buffered v.s. Unbuffered I/O
//no immediate write to file, instead buffer data and then flush after program finished
Buffered I/O may improve performance
Buffered I/O is with f...() functions
fopen(), fwrite()
Unbuffered I/O
open(), write()

18. Example: En/De-Crypter
int main ( int argc, char * argv[] ) {
FILE *in, *out;
in = fopen ( argv[1], "rb");
out = fopen ( argv[2], "wb");
if ( ! in | | ! out ){
printf( "Error opening files ! \n" );
return -1; }
while( ! feof ( in ) ){
ch = fgetc ( in );
fputc ( (ch ^ 0xFF) , out ); //UTF-16 vs UTF-8 (Unicode Byte Order mark)
} //Unicode Transformation Format
return 0;