Introduction to c part 4

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Introduction to c part 4

  1. 1. Recall • What are the difference between stack and heap? • How to allocate memory in stack? And heap? • What are the difference between malloc() and calloc()
  2. 2. Introduction to C File handling in C Week 3- day 2
  3. 3. Relevance of File handling in C
  4. 4. Relevance of File handling in C Instruction Address 11011110 00110000 00010010 00110001 10000000 00001010 01001000 10000001 00001100 10000100 11000001 00101011 01011011 01011001 11101011 11111000 Mother Board Ram Loads instruction for execution CPU Ram Stores data whenever the power is on
  5. 5. Instruction Address Ram Loads instruction for execution CPU Mother Board Relevance of File handling in C Ram looses all data whenever the power is OFF as it is volatile. So we need a mechanism to store data permanently
  6. 6. Instruction Address Ram Loads instruction for execution CPU Mother Board Relevance of File handling in C Keeps all data in a File and stores it on secondary disks such as hard disk, CD etc
  7. 7. You Should know ! Whenever we open a file it will be loaded into RAM memory . Instruction Address 11011110 00110000 00010010 00110001 10000000 00001010 01001000 10000001 00001100 10000100 11000001 00101011 01011011 01011001 11101011 11111000 Mother Board Ram Loads instruction for execution CPU
  8. 8. File Handling • Files are created for permanent storage of data • When a computer reads a file, it copies the file from the storage device to memory; when it writes to a file, it transfers data from memory to the storage device.
  9. 9. Sample Program
  10. 10. File Handling FILE *p; *p=fopen(“data.txt”,”w”) fprintf(p,“hello World”); fclose(); First you need a File pointer to the memory location where the file is loaded
  11. 11. File Handling FILE *p; *p=fopen(“data.txt”,”w”) fprintf(p,“hello World”); fclose(); Fopen() opens the file in different modes and returns the address
  12. 12. File Handling FILE *p; *p=fopen(“data.txt”,”w”) fprintf(p,“hello World”); fclose(); fprintf() is used to write in to a file same like we use printf to write on the screen
  13. 13. File Handling FILE *p; *p=fopen(“data.txt”,”r”) fprintf(p,“hello World”); fclose(p); File must be closed at the end of program using inbuilt function fclose()
  14. 14. File Modes • r : reads from a file • w : overwrite to a file • a : append on a file • r+ : reads and writes. File pointer at the beginning • w+ : reads and overwrites. • a+ : reads and appends .File pointer at the beginning
  15. 15. Write to file • fprintf(p,” hello %s”,name); • // same like printf() writes characters into a file • fputs(“message”,p); • // same purpose of fprintf() • fputc(„h‟,p); • // writes a single character into file
  16. 16. Read from File • fscanf(p,”%s”,message); • // same like scanf() reads characters from file and assign to a variable • fgets(message,100,p); • // same purpose of fscanf() but can mention the number of characters to be read • fgetc(p); • // returns the current character and advance the file pointer once; returns EOF when file ending has reached
  17. 17. #include <stdio.h> void main () { FILE *fp; int c,n=0; fp = fopen("file.txt","r"); if(fp == NULL) { printf("Error in opening file"); Exit(0); } do { c = fgetc(fp);// fgetc() always return integer .if it is character it returns corresponding integer printf("%c", c); } while(c != EOF); fclose(fp); }
  18. 18. Questions? “A good question deserve a good grade…”
  19. 19. Self Check !!
  20. 20. Self Check • The first and second arguments of fopen are a) A character string containing the name of the file & the second argument is the mode. b) A character string containing the name of the user & the second argument is the mode. c) A character string containing file poniter & the second argument is the mode. d) None of the mentioned of the mentioned
  21. 21. Self Check • The first and second arguments of fopen are a) A character string containing the name of the file & the second argument is the mode. b) A character string containing the name of the user & the second argument is the mode. c) A character string containing file poniter & the second argument is the mode. d) None of the mentioned of the mentioned
  22. 22. Self Check • If there is any error while opening a file, fopen will return a) Nothing b) EOF c) NULL d) Depends on compiler
  23. 23. Self Check • If there is any error while opening a file, fopen will return a) Nothing b) EOF c) NULL d) Depends on compiler
  24. 24. Self Check • FILE is of type ______ ? a) int type b) char * type c) struct type d) None of the mentioned
  25. 25. Self Check • FILE is of type ______ ? a) int type b) char * type c) struct type d) None of the mentioned
  26. 26. Self Check • Which of the following mode argument is used to truncate? a) a b) f c) w d) t
  27. 27. Self Check • Which of the following mode argument is used to truncate? a) a b) f c) w d) t
  28. 28. End of Day 2

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