C Preprocessing File I/O

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 3.141526 Better version #define PI ( 3.141526 ) 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*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 */ int x; /* included from myHeader.h */ • Standard header file header #ifndef MyHeaderFile_H #define MyHeaderFile_H ... /* header file contents goes here */ #endif

8. /* 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) • 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 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; }