C Programming Tutorial
printf function mainly used for printing sequence of characters on console,
printf("hello world!"); it prints string "hello World!" on the screen
Using escape character backslash(\): if you want to print string like this: sam says "I am busy tonight"
printf("sam says \"I am busy tonight\""); // escape character \ removes literal meaning of the character that it follows,here double quotaion(")
\n new line character
new line character emits string following \n to next line.
printf("hello\nHow are u?");
// prints hello
How are u?
\t horizontal tab
horizontal tab \t emits multiple spaces.
printf("h\te\tl\tl\to");
// prints
h e l l o
\v vertical tab
vertical tab \v emits string following it to next line with 1 tab space.
printf("h\ve\vl\vl\vo");
// prints
h
e
l
l
o
| Character | Output As | |
| d,i | signed decimal notation | |
| o | unsigned octal notation(without leading zero) | |
| x,X | unsgined heaxadecimal notation(without leading 0x for x, 0X for X) | |
| u | unsigned decimal notation | |
| c | Single character | |
| s | prints string until NULL character reached. | |
| f | double; decimal noation of the form [-]mmm.ddd, where d is the number of d's is given by the precision, Default is 6.precision 0 suppresses the decimal value. | |
| e,E | ||
| g,G | ||
| p | void *;print as apointer(implementation dependent) | |
| n | The number of characters written so far by this call to print is written into the argument. | |
| % | prints % |
| Character | Input Argument As | |
| d | decimal integer | |
| i | integer; the integer can be octal or hexa decimal | |
| o | octal integer(with or without) leading zero | |
| x,X | hexadecimal integer with or without leading 0x,0X | |
| u | unsigned decimal integer | |
| c | Single character | |
| s | String of non-white space characters(not quoted).char * pointing to an array of character until end of character NULL | |
| e,f,g | floating point number; | |
| p | pointer value as printed by the printf("%p") | |
| n | The number of characters written so far by this call to print is written into the argument. | |
| % | prints % | |
| % | prints % | |
| [...] | matches longest non-empty string of input characters from the set between brackets | |
| [^...] | matches longest non-empty string of input characters not from the set between brackets |
Data resides in disks,tapes in terms of files,text files,custom formatted files(word,pdf etc.,). Data can be read,write and transform using c file io functions. C file operations supports text and binary files.programmer should able to read file content,write into a file or append to a file. C file operations can be sequential or random. Sequencial means reading content from the beginning of the file to End of the file sequentially,character by character or line by line. Random access means randomly navigating to any location in the file, start extracting content.
| File Function | Description |
| fopen | opens file in specified mode for read write and append mode. file can be text or binary file. |
| fprintf | prints line of text into file |
| fscanf | reads line of text from file |
| fgetc,fgets | fgetc gets single character into file stream, fgets - gets line of text into file stream |
| fputc,fputs | fputc puts single character into file stream, fputs - puts line of text into file stream |
| fwrite | writes file data of specified size from buffer |
| fread | reads file data of specified size into buffer |
| fclose fcloseall | fclose close the current file pointer stream, fcloseall - closes all streams |
| fflush flushall | |
| ftell | ftell file pointer position |
| rewind | resets file pointer to begining of the file |
| fseek | Random access function-moves to desired location in a file |
| feof | detects end-of-file |
fopen is a function, part of stdlib.h .
FILE *fopen(const char *name, const char *mode);
fopen function takes 2 arguments , file name and mode of operation, returns file pointer.
| mode | meaning |
| r | open text file for read operation |
| w | open text file for write operation |
| a | open text file for append operation |
| rb | open binary file for read operation |
| wb | open binary file for write operation |
| ab | open binary file for append operation |
| r+ | open text file for read and write operation |
| w+ | open text file for write and read operation |
A function call to fopen, opens the file based on Mode and returns File Pointer.
File Pointer is a pointer to a structure FILE
contains information about the file. That contains information about current read pointer,Current put pointer,reserved area etc., means location of the buffer, current character position in the buffer,whether file is opened for reading or writing, whether errors or end of file have occured. etc.,
typedef struct _IO_FILE FILE; in FILE.h
FILE is a type not a structure tag.
nirvana ~> cat employees.txt Bill Thomas 8000 08/9/1968 Fred Martin 6500 22/7/1982 Julie Moore 4500 25/2/1978 Marie Jones 6000 05/8/1972 Tom Walker 7000 14/1/1977Reading a file using fopen Example:
#include <stdio.h>
int main(){
FILE * fp = fopen("employees.txt","r");
int c;
while((c=getc(fp))!=EOF){
printf("%c ",c);
}
fclose(fp);
return 0;
}
output:
Bill Thomas 8000 08/9/1968 Fred Martin 6500 22/7/1982 Julie Moore 4500 25/2/1978 Marie Jones 6000 05/8/1972 Tom Walker 7000 14/1/1977Writing to a file using fopen Example:
#include <stdio.h>
int main(){
FILE * fp = fopen("employees.txt","w");
int c;
while((c=getc(fp))!=EOF){
printf("%c ",c);
}
fclose(fp);
return 0;
}
fseek is a random access function,File pointer starts at 0, using fseek function file pointer can be moved/skip N number of bytes
fseek syntax:int fseek(FILE* fp, int offset, int origin);fseek origin values:
| Enum Name | Enum Value | Description |
| SEEK_SET | 0 | Moves the file pointer position offset bytes from the beginning of the file. |
| SEEK_CUR | 1 | Moves the file pointer position by offset bytes from current position. |
| SEEK_END | 2 | Moves the file pointer position by offset bytes from the end of the file. |
fseek returns 0 for file pointer moved sucessfully or nonzero if error occurs
Read file from last character to first character using fseek function
This example explains how to reverse each number in file called rev.txt, fopen function opens the file in read mode. fseek function goes to end of the file by using option SEEK_END, now file pointer points to one byte past to end of file, that's why used -1 for offset. ftell function tells file pointer position .i.e reading from last byte. fgetc gets character at file pointer position, decrement the offset value by one position. first byte is located at -1
$ -> cat rev.txt 123456 676666 987655
FILE *fp = fopen("rev.txt","r");
fseek(fp,-3,SEEK_END);
long l=ftell(fp);
do
{
printf("%c",fgetc(fp));
fseek(fp,l--,0);
}while(l>=-1);
output:
556789 666676 654321
#include <stdio.h>
int main(){
FILE *fp = fopen("games-country.txt","r");
char c;
int lines =0;
while( (c=fgetc(fp)) != NULL){
if(c=='\n') ++lines;
}
printf("Number of lines = %d\n",lines);
return 0;
}
#include <stdio.h>
#define MAXLENGTH 1024
int main(){
FILE *fp = fopen("games-country.txt","r");
char buffer[MAXLENGTH];
int lines =0;
while( fgets(buffer,MAXLENGTH,fp) != NULL){
++lines;
}
printf("Number of lines = %d\n",lines);
return 0;
}
/* * wordEx.c * * Created on: 03-Nov-2022 * Author: sitapathipurru */ #include#include int main() { FILE *fp = NULL; int wcount = 0; char c = '\0'; //games-country.txt fp=fopen("txt.txt","r"); int prev =0; while ((c=fgetc(fp))!=EOF){ if isspace(c) { prev=0; } else if(prev==0){wcount++;prev=1;} } printf("Number of Words = %d\n",wcount); return 0; }
For reading and writing into binary file a pair of functions are provided.
These 2 functions permit objects of any type to read or written, including Arrays and Structures
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