NetOsPgm: file operations

1. getchar() - by default read char from the stdin. return EOF if it reaches end of file
2. gets(char *buff)- by default read from stdin until new line. it will read the newline as well. return NULL if it reaches end of file
3. fgetc(FILE *fp) - read char by char from file and return EOF if it reaches end of file
4. fgets(char *buff,size_of_buffer,FILE *fp) - reads string from the file pointer until reaches new line or size_of_buffer reaches. return NULL once it reaches end of file. it will read newline as well.
5. fscanf(FILE *fp,"%d....",char *buff) - return EOF if it reaches end of the file

File handlers	functions	Return type	Example
getc	* The difference between getc() and getchar() is getc() can read from any input stream, but getchar() reads from standard input. * It reads a single character from a given input stream and returns the corresponding integer value (typically ASCII value of read character) on success. * even it reads the new line till EOF . Ex: if we give new line that also stored and printed	int getc(FILE *stream);	#include <stdio.h> int main() { printf("%c", getc(stdin)); return(0); } int in; while ((in = getchar()) != EOF) { putchar(in); }





getchar	getchar() reads from standard input. So getchar() is equivalent to getc(stdin).	int getchar(void);	#include <stdio.h> int main() { printf("%c", getchar()); return 0; }





getch	getch() is a nonstandard function and is present in conio.h header file which is mostly used by MS-DOS compilers like Turbo C.	int getch();
getche	Like getch(), this is also a non-standard function present in conio.h. It reads a single character from the keyboard and displays immediately on output screen without waiting for enter key.	int getche(void);
gets	* For reading a string value with spaces, we can use either gets() or fgets() in C * Reads characters from the standard input (stdin) and stores them as a C string into str until a newline character or the end-of-file is reached.	char * gets ( char * str );
fgets	It reads a line from the specified stream and stores it into the string pointed to by str. It stops when either (n-1) characters are read, the newline character is read, or the end-of-file is reached, whichever comes first.	char fgets(char str, int n, FILE *stream) str :Pointer to a block of memory (array of char) where the string read is copied as a C string. returns : the function returns str

Ref: https://www.geeksforgeeks.org/difference-getchar-getch-getc-getche/
https://www.geeksforgeeks.org/fgets-gets-c-language/

1. program to print the each words from the file using the fscanf

[tselva@bng-junos-d037 /b/tselva/bcopy/bk_copy_needed/copy-needed/work_tips_dir/sample_c_program]$ cat test.txt
selva kumar how are you
vithun patbitha what are you doing guys?
my name is billa 123445 selva
[tselva@bng-junos-d037 /b/tselva/bcopy/bk_copy_needed/copy-needed/work_tips_dir/sample_c_program]$ cat word.c
#include<stdio.h>
int main()
{
char word[50];
FILE *fp=fopen("test.txt","r");
while(fscanf(fp,"%s",word)!=EOF) {
printf("%s\n",word);
}

printf("\n");
return 0;
}

output:
[tselva@bng-junos-d037 /b/tselva/bcopy/bk_copy_needed/copy-needed/work_tips_dir/sample_c_program]$ ./a.out
selva
kumar
how
are
you
vithun
patbitha
what
are
you
doing
guys?
my
name
is
billa
123445

selva
https://www.quora.com/How-do-I-search-from-a-text-file-in-c-language

2. program to get the words with space using gets and split those words using sscanf from stdin

[tselva@bng-junos-d037 /b/tselva/bcopy/bk_copy_needed/copy-needed/work_tips_dir/sample_c_program]$ cat word2.c
#include<stdio.h>
#include<string.h>
int main()
{
char word[50]={0},s1[20],s2[20];
// reads the strings with spca using scanf
printf("Enter the string \n");
gets(word);
sscanf(word,"%s%s",s1,s2);
//puts(word);
puts(s1);
puts(s2);
// from the long given string split the words
printf("Enter the string \n");
fgets(word,50,stdin);
//puts(word);
char *ptr=word;
while(sscanf(ptr,"%s",s1)!=EOF) {
puts(s1);
//printf("%d\n",strlen(s1));
ptr=ptr+strlen(s1)+1;
}

printf("\n");
return 0;

}

output:

[tselva@bng-junos-d037 /b/tselva/bcopy/bk_copy_needed/copy-needed/work_tips_dir/sample_c_program]$ ./a.out
Enter the string
warning: this program uses gets(), which is unsafe.
selva kumar
selva
kumar
Enter the string
hi selva kumar how are you
hi
selva
kumar
how
are
you

3. program to get the string with space using the scanf statment itself:

[tselva@bng-junos-d037 /b/tselva/bcopy/bk_copy_needed/copy-needed/work_tips_dir/sample_c_program]$ cat word3.c

#include<stdio.h>

int main()

{

char s1[20];

printf("Enter the string \n");

scanf("%[^\n]s",s1);

puts(s1);

return 0;

}

[tselva@bng-junos-d037 /b/tselva/bcopy/bk_copy_needed/copy-needed/work_tips_dir/sample_c_program]$ ./a.out

Enter the string

selva kumar hi

selva kumar hi

Ref:https://gpraveenkumar.wordpress.com/2009/06/10/how-to-use-scanf-to-read-string-with-space/

4. program for simple fgets and simple fputs:

#include <stdio.h>
int main ( void )
{
static const char filename[] = "file.txt";
FILE *file = fopen ( filename, "r" );
if ( file != NULL )
{
char line [ 128 ]; /* or other suitable maximum line size */
while ( fgets ( line, sizeof line, file ) != NULL ) /* read a line */
{
fputs ( line, stdout ); /* write the line */
}
fclose ( file );
}
else
{
perror ( filename ); /* why didn't the file open? */
}
return 0;
}

Ref:https://www.daniweb.com/programming/software-development/code/216411/reading-a-file-line-by-line

5. program to read from the file and converting into the integer:

#include <stdio.h>   /* required for file operations */
#include <conio.h>  /* for clrscr */
#include <dos.h>  /* for delay */

FILE *fr;            /* declare the file pointer */

main()

{
   int n;
   long elapsed_seconds;
   char line[80];
   clrscr();

   fr = fopen ("elapsed.dta", "rt");  /* open the file for reading */
   /* elapsed.dta is the name of the file */
   /* "rt" means open the file for reading text */

   while(fgets(line, 80, fr) != NULL)
   {
  /* get a line, up to 80 chars from fr.  done if NULL */
  sscanf (line, "%ld", &elapsed_seconds);
  /* convert the string to a long int */
  printf ("%ld\n", elapsed_seconds);
   }
   fclose(fr);  /* close the file prior to exiting the routine */
} /*of main*/

https://www.phanderson.com/files/file_read.html

6. program to truncate newline read from the gets/fgets:

#include <stdio.h>

#include <string.h>

#define bufSize 1024

int main(int argc, char *argv[])

{

  FILE* fp;

  char buf[bufSize];

  if (argc != 2)

  {

    fprintf(stderr,

            "Usage: %s <soure-file>\n", argv[0]);

    return 1;

  }

  if ((fp = fopen(argv[1], "r")) == NULL)

  { /* Open source file. */

    perror("fopen source-file");

    return 1;

  }

  while (fgets(buf, sizeof(buf), fp) != NULL)

  {

    buf[strlen(buf) - 1] = '\0'; // eat the newline fgets() stores

    printf("%s\n", buf);

  }

  fclose(fp);

  return 0;

}

https://gsamaras.wordpress.com/code/read-file-line-by-line-in-c-and-c/

7. string matching how can we do for the given string in the file

a. using program 1 above we can take each word and do strcmp and we

can find occurence of the string

b. using program 2 above(by doing that in the file) we can take

single word and do the strcmp

c. we can do without using any library function

[tselva@bng-junos-d037 /b/tselva/bcopy/bk_copy_needed/copy-needed/work_tips_dir/sample_c_program]$ cat 1
#include<stdio.h>
#include<conio.h>
#include<stdlib.h>

count_data();

void main()
{
 // calling function
 count_data();
 getch();
}
count_data() // function for count no of words,lines & characters.
{
 FILE *fp,*fp_rep;
 char ch,ch1,temp_str[50],rep_str[10],new_str[10];
 int count=0; // counter
 clrscr();


 fp=fopen("c:\\windows\\desktop\\input.txt","r");
 fp_rep=fopen("c:\\windows\\desktop\\input1.txt","w");

 printf("\nEnter String to find:");
 scanf("%s",rep_str);
 printf("\nEnter String to replace:");
 scanf("%s",new_str);

 while((ch=getc(fp))!=EOF)
 {
  if(ch==' ')
  {
   temp_str[count]='\0';
   if(strcmp(temp_str,rep_str)==0)
   {
    printf("Do u want to replace(y/n):");
    ch1=getche();
    if(ch1=='y')
    {
     fprintf(fp_rep," %s",new_str);
     count=0;
    }
    else
    { fprintf(fp_rep," %s",temp_str);count=0;}
   }
   else
   {
    fprintf(fp_rep," %s",temp_str);
    count=0;
   }
  }else
  {
   temp_str[count++]=ch;
  }
 }
 if(strcmp(temp_str,rep_str)==0)
 {

  printf("Do u want to replace(y/n):");
  ch1=getche();
  if(ch1=='y')
  {
   fprintf(fp_rep,"%s ",new_str);
   count=0;
  }
  else
  {
   fprintf(fp_rep,"%s ",temp_str);
   count=0;
  }
 }else
 {
  fprintf(fp_rep,"%s ",temp_str);
 }

 fclose(fp);
 fclose(fp_rep);
 remove("c:\\windows\\desktop\\input.txt");
 rename("c:\\windows\\desktop\\input1.txt","c:\\windows\\desktop\\input.txt");
 fflush(stdin);
[tselva@bng-junos-d037 /b/tselva/bcopy/bk_copy_needed/copy-needed/work_tips_dir/sample_c_program]$
[tselva@bng-junos-d037 /b/tselva/bcopy/bk_copy_needed/copy-needed/work_tips_dir/sample_c_program]$

8. split strings based on any delimiter is :

#include <string.h>

#include <stdio.h>

int main()
{
   char str[80] = "This is - www.tutorialspoint.com - website";
   const char s[2] = "-";
   char *token;
   
   /* get the first token */
   token = strtok(str, s);
   
   /* walk through other tokens */
   while( token != NULL ) 
   {
      printf( " %s\n", token );
    
      token = strtok(NULL, s);
   }
   
   return(0);
}

https://www.tutorialspoint.com/c_standard_library/c_function_strtok.htm

9. program to club two lines from two files:


#include <stdio.h>


int main() {
  char c[78];  /* declare a char array */
  char d[6];
  char e[90];
  FILE *file,*filep,*file2;  /* declare a FILE pointer  */


  file = fopen("data.txt", "r");
  file2 = fopen("data2.txt", "r");
  filep = fopen("dataprint.txt","w+");


  /* open a text file for reading */


  
    while(fgets(c, 78, file)!=NULL && fgets (d,6,file2)!=NULL) { 


      concat (e,d,c);//fist attempt
      fprintf(filep,"%s",e);
      
      //fprintf(filep,"%s %s",d,c); //second attempt  


    }


    printf("\n\nClosing file...\n");
    fclose(file);
    fclose(file2);
    fclose(filep);
    system("pause");
    return 0;


  }

https://www.daniweb.com/programming/software-development/threads/193980/combine-two-txt-file-line-by-line-using-fgets

REf: http://beej.us/guide/bgc/output/html/multipage/gets.html

http://people.cs.uchicago.edu/~dmfranklin/tutorials/fgets.txt

10. program for getc & getchar:

#include <stdio.h>
void read_single_char() {
   printf("%c", getc(stdin));
}
void read_single_till_eof_stdin () {
   int i=0;
   char stream[128] = {0};
   while((stream[i] = getc(stdin)) != EOF) {
         i++;
         if(i > 30) {
           break;
         }
   }
   printf("%s\n", stream);
}

int main()
{
   //read_single_char();
   read_single_till_eof_stdin();
   return(0);
}

output:

tselva@tselva-mbp:~/Documents/work/c> ./a.out
hi
selva
kumar
how
are you
this is the end of the world
hi
selva
kumar
how
are you
th

11. finding the number of occurence of the word using fscanf :

#include<stdio.h>
#include<string.h>
#include<stdlib.h>

int main (int argc,char *argv[]) {
        char occur[1000][256]={0};
        int i=0,j=0;
        char matching_word[50];
        int count=0;
        if (argc != 3) {
                printf("<prog> <file_name> <matching_string>\n");
                exit(0);
        }
        FILE *fp=fopen(argv[1],"r");
        strcpy(matching_word,argv[2]);

        while((fscanf(fp,"%s",occur[i]) != EOF) && (i < 1000)) {
                //printf("%s\n",occur[i]);
                i++;
        }

        for(j=0;j<i;j++) {
            //printf("%s\n",occur[j]);
            if(strcmp(occur[j],matching_word) == 0) {
                    count++;
            }
        }
        printf("\nmatching word %s occurence - %d\n",matching_word,count);

}


output:

tselva@tselva-mbp:~/Documents/work/c> ./a.out test.txt selva

matching word selva occurence - 0
tselva@tselva-mbp:~/Documents/work/c> ./a.out test.txt you

matching word you occurence - 6
tselva@tselva-mbp:~/Documents/work/c> more test.txt
hi
how are you
how are you
this is the end of the world
you you you you

NetOsPgm

Tuesday, August 8, 2017

file operations

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