~Help - File processing with user input~

**indy** · 12-02-2003

Hi all

This may sound like a silly/simply question how do i create a file from user input e.g. i want the user to input a file name and that input creates a file with same name...

required output...

1.Input file name to process: xyz (this xyz is created)then
i want to make sure the entry is made, if blank output a message..

2. which line no. to enter the data into...

3. Enter text....prompt user to ok to continue if no quit

4.if yes enter the text into the line no. and display it ...

i would appreciate if someone can give a c program script to get me started, thanks in advance....i am new to c programming...thanks again...indy

**Prelude** · 12-02-2003

Here is some code to open a file for writing (creating it if necessary) and add some arbitrary text to it. You can use this to develop your own solution based on your needs.

Code:

FILE *out;
char filename[FILENAME_MAX];
char text[BUFSIZ];

printf ( "Enter a file to create: " );
fflush ( stdout );
if ( fgets ( filename, sizeof filename, stdin ) != NULL ) {
  char *newline = strrchr ( filename, '\n' );

  if ( newline != NULL )
    *newline = '\0';
  out = fopen ( filename, "w" );
  if ( out == NULL ) {
    perror ( "File open failure" );
    return EXIT_FAILURE;
  }
  printf ( "Enter text for your new file: " );
  fflush ( stdout );
  if ( fgets ( text, sizeof text, stdin ) != NULL )
    fputs ( text, stream );
  fclose ( out );
}

**indy** · 12-02-2003

hi prelude

thanks for the reply, but this is what i want to do , sorry i did not explain properly...

i want to enabling a user to insert a line in a specific part of a text file, i.e.
- ask user the name of the file,
- ask user where (line number) s/he wants to insert the line
- ask user to provide the text for this line

You then insert this line into the specific part of the file and ask user whether s/he wants to continue or not.

i would appreciate any sort of code snippet/script, i have tommorrow to finish it ...waiting for reply....thanks again...indy

**Prelude** · 12-02-2003

>ask user the name of the file
Already answered.

>ask user where (line number) s/he wants to insert the line
You can find the answer to this in the FAQ.

>ask user to provide the text for this line
Already answered.

But it strikes me that these three requirements are not your problem. What you really want to know is how to insert a line of text into an indexed file. The answer is that it would be easier to read the entire contents of the file into memory, then insert your new line at the desired location and rewrite the data back to the file:

Code:

i = 0
while not eof
  read a line
  add the line to a linked list
  i = i + 1;
  if i == line_number
    add new line to the linked list
  endif
loop
# Reopen the file for writing
while list not empty
  write a line to the file
  remove a line from the linked list
loop

**indy** · 12-02-2003

hi there prelude

thanks for the logic, what i was thinking is would it not be better to check if the file exists or prompt the user to read the text file, if y continue then abort...code would appreciated...thanks in advance...indy

Code:

i = 0
while not eof
  read a line
  add the line to a linked list
  i = i + 1;
  if i == line_number
    add new line to the linked list
  endif
loop
# Reopen the file for writing
while list not empty
  write a line to the file
  remove a line from the linked list
loop

**Prelude** · 12-02-2003

>would it not be better to check if the file exists or prompt the user to read the text file
Yes, it would. That way you don't throw away anything in an already existing file. To test if a file exists, simply try to open it for reading. If fopen fails, the file most likely doesn't exist, so you can then go right to the writing step. Otherwise, follow the logic I gave earlier.

>code would appreciated
The code is trivial, I'm sure you can handle it.

**indy** · 12-02-2003

Hi there prelude...

thanks for the reply, heres my code so far, i want to incoperate my previous logic...i real sloww in getting it into script and i need more help...thanks...indy

Code:

#include "stdio.h"
#include "stdlib.h"

void main(void)
{
 FILE *fp;
 char fname[128];

 printf("Enter filename: ");
 gets(fname);

 if((fp=fopen(fname, "r"))==NULL) {
 printf("cannot open file\n");
 exit(1);
}

fclose(fp);
}

**quzah** · 12-02-2003

It's a good start, with a couple of problems:
1) 'main' always returns an int, not void. Thus, your main function should be:

Code:

int main( void )
{
    ...code...

    return 0;
}

2) You shouldn't use gets, because it has problems also. Such as, it doesn't check input size, so it's abusable and can cause your program to crash. It doesn't safety check the input size, so it likes to ramble off the end of your array and corrupt your application.

You should use fgets instead. Consider reading this FAQ entry on how to correctly read a line from a user.

From there, see what else you can come up with, and we'll point you in the right direction.

Quzah.

**indy** · 12-03-2003

Hi ther quaze

thanks for the reply,hint...much appreciated, i have the code below which i want to modify so that i can prompt the user with the following while reading a file into memory..

1. enabling a user to insert a line in a specific part of a text file, i.e.
- prompt user the name of the file,
- prompt user where (line number) s/he wants to insert the line
- prompt user to provide the text for this line

then i want to insert this line into the specific part of the file and ask user whether s/he wants to continue or not.

the code below works but only prompts the user new number to be added, adds it and lists the contents of the whole file...how can i modify it to ask for the above user inputs...feel free to modify ...thanks in advance...indy

Code:

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

/* Define the maximum value e.g. 20 in this case.*/

#define MAX 20

int main ( void )

/* File/Integer declarations.*/

{
  FILE *io;
  int  file[BUFSIZ];
  int  i, j;
  int  new_item;

/* Reading the input file with read mode.*/

  io = fopen ( "file.txt", "r" );

/* Open file failure error routines.*/

  if ( io == NULL ) {
    perror ( "File open failure" );
    return EXIT_FAILURE;
}
  i = 0;
  while ( fscanf ( io, "%d%*c", &file[i] ) == 1 )
    i++;
  fclose ( io );

/* User input declaration.*/

  printf ( "Enter a new number to be added to the file..: " );
  fflush ( stdout );

/* Output Buffer setup.*/

  if ( scanf ( " %d", &new_item ) != 1 ) {
    fprintf ( stderr, "Sorry Invalid input, please try again..!!" );
    return EXIT_FAILURE;
}
  io = fopen ( "file.txt", "w" );
  if ( io == NULL ) {
    perror ( "File open failure" );
    return EXIT_FAILURE;

/* New entry input & modifications and output to screen.*/

}
  for ( j = 0; j < i && file[j] <= new_item; j++ ) {
    fprintf ( io, "%d,", file[j] );
    printf ( "%d,", file[j] );
}
  fprintf ( io, "%d,", new_item );
  printf ( "%d,", new_item );
  for ( ; j < i; j++ ) {
    fprintf ( io, "%d,", file[j] );
    printf ( "%d,", file[j] );
}
  fclose ( io );

  return EXIT_SUCCESS;
}

thanks again...indy

**WaltP** · 12-03-2003

Well,
[i]while ( fscanf ( io, "%d%*c", &file ) == 1 )
The fscanf() format "%d%*c" requires 3 parameters, you supplied 1. The %d gets placed in the i'th byte in file, the rest are lost.

Also, all the while loop does is populate the entire file buffer with the integer in the first postition of each line of the file.

As far as

1. enabling a user to insert a line in a specific part of a text file, i.e.
- prompt user the name of the file,
- prompt user where (line number) s/he wants to insert the line
- prompt user to provide the text for this line

Tips:
do NOT use scanf -- at all! Use fgets for all input (file and user) to prevent unexpected results. Examples are all over this forum -- search them out, check the FAQ

Reread Prelude's first post -- she gave you most of what you need.

**indy** · 12-04-2003

hi there

thanks walt p ...i bit confused and having problems with adding text for a line number...had a look at the faq/archive but still having problems, my code below, does ask for file name and line number to add text but does not insert the text to that line number, have used cput,cget to add text, where is it i am going wrong...now it does not compile either...sorry...thanks in advance...i am too sloww for this group...sorry

Code:

#include "stdio.h"
#include "stdlib.h"

void main(void)
{
  FILE *fp;
  char s[80];
  int t;
  char p[23];/* for text for line number.*/
  s[0] = 20;

  if ((fp = fopen("test", "w")) == NULL) {
   printf("sorry...cannot open file.. !!\n");
   exit(1);
}

 printf("Enter file name & Line Number to insert data.. : ");

/* Read from keyboard. */

 /*fscanf(stdin, "%s%d", s, &t);*/

   fscanf(stdin, "%s%d", s, &t, "%p%d", p);
  /* read text for the location.*/

  cputs("Enter text for Line number to  insert.. : ");
  cgets(s);
  cputs(&s[2]);

/*write to file.*/

   fprintf(fp, "%s %d", s, t);

   fclose(fp);

   if((fp=fopen("test", "r")) == NULL){
    printf("sorry...cannot open file.. !!\n");
    exit(1);

/* read from a file.*/

   fscanf(fp, "%s%d", s, &t);

/* print to screen.*/

   fprintf(stdout, "%s %d", s, t, p);
}

thanks in advance...indy

**Prelude** · 12-04-2003

You've clearly butchered the code you've been given thusfar. Why don't you try starting over with the complete program I provided you that does what you want with a file of integers. All you need to do is modify it to use strings instead, and the FAQ tells you how to read and write strings correctly.

**indy** · 12-04-2003

hi prelude...

thanks...but i am bit confused and have alot of versions , yes i have well butchered it u are right, could u please start me off again....heres what i want to do...

enabling a user to insert a line in a specific part of a text file, i.e.
1-ask user the name of the file,
2- ask user where (line number) s/he wants to insert the line
3.ask user to provide the text for this line
4.then insert this line into the specific part of the file and ask user whether s/he wants to continue or not.

thanks again...indy

**indy** · 12-04-2003

hi prelude

this is what i have from scartch...

Code:

#include <stdio.h>

#define MAX 10
#define LEN 80

char text[MAX][LEN];
FILE *openinfile(void);

void main(void)
{
        register int t,i,j;
        int n,row,p,x;
        char y[80];
        FILE * fp;
        n=0;

        fp = openinfile();
        for (row=0;row<10;row++)
        {
                fgets(text[row],LEN,fp);
        }
        fclose(fp);

        for(i=0;i<MAX;i++)
        {
                for(j=0; text[i][j];j++) putchar(text[i][j]);
        }

        printf("Enter text line to edit : \n");
        scanf("%d", &n);

        printf("Line selected is : %s\n", text[n]);

        printf("Enter text for line....\n");
        gets(text[n]);
        if(!*text[n]) gets(text[n]);

 for(i=0;i<MAX;i++)
        {
                for(j=0; text[i][j];j++) putchar(text[i][j]);
        }
}

FILE *openinfile(void)
{
        FILE *fp;
        char infile[25];

        printf("Input filename : ");
        gets(infile);
        fp = fopen(infile, "r");
        return fp;
}

**Prelude** · 12-04-2003

>could u please start me off again....
Make sure you understand this completely before making any changes.

Code:

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

#define MAX 20

int main ( void )
{
  char file[MAX][BUFSIZ];
  char new_item[BUFSIZ];
  FILE *io;
  int  pos;
  int  i;
  int  j;

  for ( ; ; ) {
    io = fopen ( "input.txt", "r" );
    if ( io == NULL ) {
      perror ( "File open failure" );
      return EXIT_FAILURE;
    }
    for ( i = 0; fgets ( file[i], MAX, io ) != NULL; i++ )
      ;
    fclose ( io );
    printf ( "Enter new text to be added to the file..: " );
    fflush ( stdout );
    if ( fgets ( new_item, sizeof new_item, stdin ) == NULL ) {
      fprintf ( stderr, "Invalid input" );
      return EXIT_FAILURE;
    }
    printf ( "Enter the location to insert the new text: " );
    fflush ( stdout );
    if ( scanf ( " %d", &pos ) != 1 ) {
      fprintf ( stderr, "Invalid input" );
      return EXIT_FAILURE;
    }
    if ( pos < 0 )
      pos = 0;
    if ( pos > i )
      pos = i;
    io = fopen ( "input.txt", "w" );
    if ( io == NULL ) {
      perror ( "File open failure" );
      return EXIT_FAILURE;
    }
    for ( j = 0; j < pos; j++ ) {
      fprintf ( io, "%s", file[j] );
      printf ( "%s", file[j] );
    }
    fprintf ( io, "%s", new_item );
    printf ( "%s", new_item );
    for ( ; j < i; j++ ) {
      fprintf ( io, "%s", file[j] );
      printf ( "%s", file[j] );
    }
    fclose ( io );
    printf ( "Add another line? (y/n): " );
    if ( tolower ( getchar() ) != 'y' )
      break;
    while ( getchar() != '\n' )
      ;
  }

  return EXIT_SUCCESS;
}

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~Help - File processing with user input~

~thanks prelude - more help please~

~ thanks yes but ~

~ More help on my code prelude~

~ More help !!..code not working~

thanks - sloww coder...need more help..

~ sorry - was bit lost !!~

~ new code ...from scratch...

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