Write to file

[Bill]

Hello,

I'm trying to output buffer content to a file. I either get an access
violation error, or crazy looking output in the file depending on
which method I use to write the file. Can anyone help out a newbie?
#include <stdio.h>
#include <ctype.h>
#include <string.h>

#define DISPLAY 117 /* Length of display line */
#define PAGE_LENGTH 20 /* Lines per page */

int main(int argc, char *argv[])
{
FILE *pfile;
FILE *outfile;
char *p;

unsigned char buffer[DISPLAY/4 - 1]; /* File input buffer */
int count = 0; /* Count of characters in buffer */
int lines = 0; /* Number of lines displayed */
int i = 0; /* Loop counter */

char string [100];
pfile = fopen ("my.txt" , "r");

while(!feof(pfi le)) /* Continue until end of file */
{
if(count < sizeof buffer) /* If the buffer is not full */
/* Read a character */
buffer[count++] = (unsigned char)fgetc(pfil e);
else
{
/* Now display buffer contents as characters */
for(count = 0; count < sizeof buffer; count++)
printf("%c", isprint(buffer[count]) ? buffer[count]:'.');
printf("\n"); /* End the line */
count = 0; /* Reset count */

if(!(++lines%PA GE_LENGTH)) /* End of page? */
if(getchar()==' E') /* Wait for Enter */
return 0; /* E pressed */
}
}

/* Display last line as characters */
for(i = 0; i < count; i++)
{
printf("%c",isp rint(buffer[i]) ? buffer[i]:'.');
}

printf("\n");
fclose(pfile); /* Close the file */

//re-open file and write out the buffer contents
outfile = fopen ("myOutput.t xt" , "w");

if(outfile==NUL L)
{
return 0;
}

//causes an access violation error
for(count = 0; count < sizeof buffer; count++)
{
fputc(outfile, isprint(buffer[count]) ? buffer[count]:'.');
}

//causes crazy output in file
/*for(count = 0; count < sizeof buffer; count++)
{
(int) fwrite(buffer, 1, isprint(buffer[count]), outfile);
}*/

fclose(outfile) ;
getchar();
return 0;
}

[Ben Bacarisse]

Bill <bi*********@al lstate.comwrite s:

Hello,

I'm trying to output buffer content to a file. I either get an access
violation error, or crazy looking output in the file depending on
which method I use to write the file. Can anyone help out a newbie?

Sure...

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

#define DISPLAY 117 /* Length of display line */
#define PAGE_LENGTH 20 /* Lines per page */

int main(int argc, char *argv[])
{
FILE *pfile;
FILE *outfile;
char *p;

unsigned char buffer[DISPLAY/4 - 1]; /* File input buffer */
int count = 0; /* Count of characters in buffer */
int lines = 0; /* Number of lines displayed */
int i = 0; /* Loop counter */

char string [100];
pfile = fopen ("my.txt" , "r");

You should check it worked. I know you know this!

while(!feof(pfi le)) /* Continue until end of file */

This will cause you some surprises and won't do what you think. You
should check the return from the read operation (in you case) fgetc:

int c;
....
while ((c = fgetc(pfile)) != EOF) {
...

The feof function only returns a non-zero value *after* an input
operation has failed due to and end-of-file condition. It should be
used only to tell *why* things have gone wrong.

{
if(count < sizeof buffer) /* If the buffer is not full */
/* Read a character */
buffer[count++] = (unsigned char)fgetc(pfil e);
else
{
/* Now display buffer contents as characters */
for(count = 0; count < sizeof buffer; count++)
printf("%c", isprint(buffer[count]) ? buffer[count]:'.');
printf("\n"); /* End the line */
count = 0; /* Reset count */

if(!(++lines%PA GE_LENGTH)) /* End of page? */
if(getchar()==' E') /* Wait for Enter */
return 0; /* E pressed */

There getchar calls will normally be working on a buffered input so it
is not a good way to "pause" your program. If I wanted to do this (and
for some reason I don't these days) I'd write a function to read a
whole line of input and decide what to do based on that.

}
}

/* Display last line as characters */
for(i = 0; i < count; i++)
{
printf("%c",isp rint(buffer[i]) ? buffer[i]:'.');
}

printf("\n");
fclose(pfile); /* Close the file */

You should check if this worked also.

//re-open file and write out the buffer contents
outfile = fopen ("myOutput.t xt" , "w");

if(outfile==NUL L)
{
return 0;
}

//causes an access violation error
for(count = 0; count < sizeof buffer; count++)
{
fputc(outfile, isprint(buffer[count]) ? buffer[count]:'.');

You should check that this worked. Get in the habit of checking
everything that there is to check!

}

//causes crazy output in file
/*for(count = 0; count < sizeof buffer; count++)
{
(int) fwrite(buffer, 1, isprint(buffer[count]), outfile);
}*/

This will repeatedly try to print the first character in buffer as
many times as there are printable characters in the buffer!. Also, by
using it this way (asking to write no data sometimes) you make error
checking much harder. Stick with the fputc method. It is fine. For
the record you probably intended:

fwrite(&buffer[count], 1, isprint(buffer[count]), outfile);

If you want to print a whole buffer. Process it first:

for (count = 0; count < sizeof buffer; count++)
if (!isprint(buffe r[count]))
buffer[count] = '.';

if (fwrite(buffer, 1, count, outfile) != count)
/* report a write error... */

>
fclose(outfile) ;
getchar();
return 0;
}

--
Ben.

[Bill]

On Jun 13, 6:09 am, Ben Bacarisse <ben.use...@bsb .me.ukwrote:

Bill <bill.war...@al lstate.comwrite s:

Hello,

I'm trying to output buffer content to a file. I either get an access
violation error, or crazy looking output in the file depending on
which method I use to write the file. Can anyone help out a newbie?

Sure...

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

#define DISPLAY 117 /* Length of display line */
#define PAGE_LENGTH 20 /* Lines per page */

int main(int argc, char *argv[])
{
FILE *pfile;
FILE *outfile;
char *p;

unsigned char buffer[DISPLAY/4 - 1]; /* File input buffer */
int count = 0; /* Count of characters in buffer */
int lines = 0; /* Number of lines displayed */
int i = 0; /* Loop counter */

char string [100];
pfile = fopen ("my.txt" , "r");

You should check it worked. I know you know this!

while(!feof(pfi le)) /* Continue until end of file */

This will cause you some surprises and won't do what you think. You
should check the return from the read operation (in you case) fgetc:

int c;
....
while ((c = fgetc(pfile)) != EOF) {
...

The feof function only returns a non-zero value *after* an input
operation has failed due to and end-of-file condition. It should be
used only to tell *why* things have gone wrong.

{
if(count < sizeof buffer) /* If the buffer is not full */
/* Read a character */
buffer[count++] = (unsigned char)fgetc(pfil e);
else
{
/* Now display buffer contents as characters */
for(count = 0; count < sizeof buffer; count++)
printf("%c", isprint(buffer[count]) ? buffer[count]:'.');
printf("\n"); /* End the line */
count = 0; /* Reset count */

if(!(++lines%PA GE_LENGTH)) /* End of page? */
if(getchar()==' E') /* Wait for Enter */
return 0; /* E pressed */

There getchar calls will normally be working on a buffered input so it
is not a good way to "pause" your program. If I wanted to do this (and
for some reason I don't these days) I'd write a function to read a
whole line of input and decide what to do based on that.

}
}

/* Display last line as characters */
for(i = 0; i < count; i++)
{
printf("%c",isp rint(buffer[i]) ? buffer[i]:'.');
}

printf("\n");
fclose(pfile); /* Close the file */

You should check if this worked also.

//re-open file and write out the buffer contents
outfile = fopen ("myOutput.t xt" , "w");

if(outfile==NUL L)
{
return 0;
}

//causes an access violation error
for(count = 0; count < sizeof buffer; count++)
{
fputc(outfile, isprint(buffer[count]) ? buffer[count]:'.');

You should check that this worked. Get in the habit of checking
everything that there is to check!

}

//causes crazy output in file
/*for(count = 0; count < sizeof buffer; count++)
{
(int) fwrite(buffer, 1, isprint(buffer[count]), outfile);
}*/

This will repeatedly try to print the first character in buffer as
many times as there are printable characters in the buffer!. Also, by
using it this way (asking to write no data sometimes) you make error
checking much harder. Stick with the fputc method. It is fine. For
the record you probably intended:

fwrite(&buffer[count], 1, isprint(buffer[count]), outfile);

If you want to print a whole buffer. Process it first:

for (count = 0; count < sizeof buffer; count++)
if (!isprint(buffe r[count]))
buffer[count] = '.';

if (fwrite(buffer, 1, count, outfile) != count)
/* report a write error... */

fclose(outfile) ;
getchar();
return 0;
}

--
Ben.- Hide quoted text -

- Show quoted text -

Thanks alot. I'm making progress. No errors now, but the output in
the file is screwy. The code:
#include <stdio.h>
#include <ctype.h>
#include <string.h>

#define DISPLAY 117 /* Length of display line */
#define PAGE_LENGTH 20 /* Lines per page */

int main(int argc, char *argv[])
{
FILE *pfile; /* File pointer */
FILE *outfile;
char *p;
int c;

unsigned char buffer[DISPLAY/4 - 1]; /* File input buffer */
int count = 0; /* Count of characters in buffer */
int lines = 0; /* Number of lines displayed */
int i = 0; /* Loop counter */

char string [100];
pfile = fopen ("my.txt" , "r");
while((c = fgetc(pfile)) != EOF) /* Continue until end of
file */
{
if(count < sizeof buffer) /* If the buffer is not full */
/* Read a character */
buffer[count++] = (unsigned char)fgetc(pfil e);
else
{
/* Now display buffer contents as characters */
for(count = 0; count < sizeof buffer; count++)
printf("%c", isprint(buffer[count]) ? buffer[count]:'.');
printf("\n"); /* End the line */
count = 0; /* Reset count */

if(!(++lines%PA GE_LENGTH)) /* End of page? */
if(getchar()==' E') /* Wait for Enter */
return 0; /* E pressed */
}
}

/* Display last line as characters */
for(i = 0; i < count; i++)
{
printf("%c",isp rint(buffer[i]) ? buffer[i]:'.');
}

printf("\n");
fclose(pfile); /* Close the file */

//re-open file and write out the buffer contents
outfile = fopen ("myOutput.t xt" , "w");

if(outfile==NUL L)
{
return 0;
}
for(count = 0; count < sizeof buffer; count++)
{
if(!isprint(buf fer[count]))
{
buffer[count] = '.';
}
else
{
fputc(buffer[count],outfile);
}
//fputc(outfile, isprint(buffer[count]) ? buffer[count]:'.');
}

/*for(count = 0; count < sizeof buffer; count++)
{
(int) fwrite(buffer, 1, isprint(buffer[count]), outfile);
}*/

fclose(outfile) ;
getchar();
return 0;
}

Input file contents:
Fred Flinstone 123-456-7890
Barney Rubble 123-789-4561

Output file:
B12y7p456r

[Ben Bacarisse]

Bill <bi*********@al lstate.comwrite s:

Thanks alot. I'm making progress. No errors now, but the output in
the file is screwy. The code:

Please trip your replies (and always trim signature lines).

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

#define DISPLAY 117 /* Length of display line */
#define PAGE_LENGTH 20 /* Lines per page */

int main(int argc, char *argv[])
{
FILE *pfile; /* File pointer */
FILE *outfile;
char *p;
int c;

unsigned char buffer[DISPLAY/4 - 1]; /* File input buffer */
int count = 0; /* Count of characters in buffer */
int lines = 0; /* Number of lines displayed */
int i = 0; /* Loop counter */

char string [100];
pfile = fopen ("my.txt" , "r");
while((c = fgetc(pfile)) != EOF) /* Continue until end of
file */
{
if(count < sizeof buffer) /* If the buffer is not full */
/* Read a character */
buffer[count++] = (unsigned char)fgetc(pfil e);

I intended you you use c here not read another character!

else
{
/* Now display buffer contents as characters */
for(count = 0; count < sizeof buffer; count++)
printf("%c", isprint(buffer[count]) ? buffer[count]:'.');
printf("\n"); /* End the line */
count = 0; /* Reset count */

Your input is long enough to trigger this condition. You reuse the buffer.

if(!(++lines%PA GE_LENGTH)) /* End of page? */
if(getchar()==' E') /* Wait for Enter */
return 0; /* E pressed */
}
}

/* Display last line as characters */
for(i = 0; i < count; i++)
{
printf("%c",isp rint(buffer[i]) ? buffer[i]:'.');
}

printf("\n");
fclose(pfile); /* Close the file */

//re-open file and write out the buffer contents
outfile = fopen ("myOutput.t xt" , "w");

if(outfile==NUL L)
{
return 0;
}
for(count = 0; count < sizeof buffer; count++)
{
if(!isprint(buf fer[count]))
{
buffer[count] = '.';
}
else
{
fputc(buffer[count],outfile);
}

You took a suggestion to modify the buffer and combined it with single
character printing to produce something rather odd. It is not wrong,
just odd. Why change buffer[count] when is it not a printing
character if you don't then print it?

//fputc(outfile, isprint(buffer[count]) ? buffer[count]:'.');
}

/*for(count = 0; count < sizeof buffer; count++)
{
(int) fwrite(buffer, 1, isprint(buffer[count]), outfile);
}*/

fclose(outfile) ;
getchar();
return 0;
}

Input file contents:
Fred Flinstone 123-456-7890
Barney Rubble 123-789-4561

Output file:
B12y7p456r

Not what I get, but still.

I should point out that although I have only commented on details, the
overall design of this program looks a bit wacky. If you intend to
process text files, why do you have a buffer of size 117/4-1? Why are
you happy to simply reuse the space when you read more than these 28
characters? If the input has 30 characters, your buffer will contain
numbers 29 and 30 followed by character numbers 3, 4 and so on. It
all looks very odd.

You should maybe say what you are actually trying to do.

--
Ben.

[Bill]

On Jun 13, 7:40 am, Ben Bacarisse <ben.use...@bsb .me.ukwrote:

Bill <bill.war...@al lstate.comwrite s:

Thanks alot. I'm making progress. No errors now, but the output in
the file is screwy. The code:

Please trip your replies (and always trim signature lines).

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

#define DISPLAY 117 /* Length of display line */
#define PAGE_LENGTH 20 /* Lines per page */

int main(int argc, char *argv[])
{
FILE *pfile; /* File pointer */
FILE *outfile;
char *p;
int c;

unsigned char buffer[DISPLAY/4 - 1]; /* File input buffer */
int count = 0; /* Count of characters in buffer */
int lines = 0; /* Number of lines displayed */
int i = 0; /* Loop counter */

char string [100];
pfile = fopen ("my.txt" , "r");

while((c = fgetc(pfile)) != EOF) /* Continue until end of
file */
{
if(count < sizeof buffer) /* If the buffer is not full */
/* Read a character */
buffer[count++] = (unsigned char)fgetc(pfil e);

I intended you you use c here not read another character!

else
{
/* Now display buffer contents as characters */
for(count = 0; count < sizeof buffer; count++)
printf("%c", isprint(buffer[count]) ? buffer[count]:'.');
printf("\n"); /* End the line */
count = 0; /* Reset count */

Your input is long enough to trigger this condition. You reuse the buffer.

if(!(++lines%PA GE_LENGTH)) /* End of page? */
if(getchar()==' E') /* Wait for Enter */
return 0; /* E pressed */
}
}

/* Display last line as characters */
for(i = 0; i < count; i++)
{
printf("%c",isp rint(buffer[i]) ? buffer[i]:'.');
}

printf("\n");
fclose(pfile); /* Close the file */

//re-open file and write out the buffer contents
outfile = fopen ("myOutput.t xt" , "w");

if(outfile==NUL L)
{
return 0;
}

for(count = 0; count < sizeof buffer; count++)
{
if(!isprint(buf fer[count]))
{
buffer[count] = '.';
}
else
{
fputc(buffer[count],outfile);
}

You took a suggestion to modify the buffer and combined it with single
character printing to produce something rather odd. It is not wrong,
just odd. Why change buffer[count] when is it not a printing
character if you don't then print it?

//fputc(outfile, isprint(buffer[count]) ? buffer[count]:'.');
}

/*for(count = 0; count < sizeof buffer; count++)
{
(int) fwrite(buffer, 1, isprint(buffer[count]), outfile);
}*/

fclose(outfile) ;
getchar();
return 0;
}

Input file contents:
Fred Flinstone 123-456-7890
Barney Rubble 123-789-4561

Output file:
B12y7p456r

Not what I get, but still.

I should point out that although I have only commented on details, the
overall design of this program looks a bit wacky. If you intend to
process text files, why do you have a buffer of size 117/4-1? Why are
you happy to simply reuse the space when you read more than these 28
characters? If the input has 30 characters, your buffer will contain
numbers 29 and 30 followed by character numbers 3, 4 and so on. It
all looks very odd.

You should maybe say what you are actually trying to do.

--
Ben.- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -

Yes. It has become wacky. What I'm trying to do is read the contents
of a file into a buffer, find a particular string in the buffer, make
an edit in the found string and write the same file back out.

[Ben Bacarisse]

Bill <bi*********@al lstate.comwrite s:

On Jun 13, 7:40 am, Ben Bacarisse <ben.use...@bsb .me.ukwrote:

>You should maybe say what you are actually trying to do.

Yes. It has become wacky. What I'm trying to do is read the contents
of a file into a buffer, find a particular string in the buffer, make
an edit in the found string and write the same file back out.

Ah, well... that could be done much more simply. Presumably this is some
class assignment or you would simply use one of the many fine tools
that can do this?

You did not take my advice to trim your replies (you quoted everything
including my signature block). That will have won you no favours from
others here and it discourages me from helping further.

--
Ben.

[Bill]

>
You did not take my advice to trim your replies (you quoted everything
including my signature block). That will have won you no favours from
others here and it discourages me from helping further.

Sorry. Yes it is an assignment, but I'm trying to take it further
than what was assigned.
I really wish to learn the language.

[Bryan]

On 13 Jun, 13:04, Bill <bill.war...@al lstate.comwrote :

>
Thanks alot. I'm making progress. No errors now, but the output in
the file is screwy. The code:

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

#define DISPLAY 117 /* Length of display line */
#define PAGE_LENGTH 20 /* Lines per page */

int main(int argc, char *argv[])
{
FILE *pfile; /* File pointer */
FILE *outfile;
char *p;
int c;

unsigned char buffer[DISPLAY/4 - 1]; /* File input buffer */

Initialising this would be advisable, given what you're going to do
with it later.

int count = 0; /* Count of characters in buffer */
int lines = 0; /* Number of lines displayed */
int i = 0; /* Loop counter */

char string [100];
pfile = fopen ("my.txt" , "r");

while((c = fgetc(pfile)) != EOF) /* Continue until end of
file */
{
if(count < sizeof buffer) /* If the buffer is not full */
/* Read a character */
buffer[count++] = (unsigned char)fgetc(pfil e);

This needs to be changed to :
buffer[count++] = (unsigned char)c;

As otherwise you are reading the first character in the while loop and
then ignoring it and reading a second character here. This is why you
get every other character in the output.

else
{
/* Now display buffer contents as characters */
for(count = 0; count < sizeof buffer; count++)
printf("%c", isprint(buffer[count]) ? buffer[count]:'.');
printf("\n"); /* End the line */
count = 0; /* Reset count */

This is what's causing your output file to look a bit odd. Once you've
read the input up to a full buffer, you just print it to screen and
then re-start at the beginning of the buffer. This data never (except
for the last couple of rows, by chance) goes to the datafile and so
you don't get everything that you're after. So you either need to
output it here or store it somehow.

>
if(!(++lines%PA GE_LENGTH)) /* End of page? */
if(getchar()==' E') /* Wait for Enter */
return 0; /* E pressed */
}
}

/* Display last line as characters */
for(i = 0; i < count; i++)
{
printf("%c",isp rint(buffer[i]) ? buffer[i]:'.');
}

printf("\n");
fclose(pfile); /* Close the file */

//re-open file and write out the buffer contents
outfile = fopen ("myOutput.t xt" , "w");

if(outfile==NUL L)
{
return 0;
}

for(count = 0; count < sizeof buffer; count++)

You also don't know that all of buffer has been filled. It's not
initialised so it could well be causing undefince behaviour here. You
either need to keep a count of how many characters you've read or need
to initialise the array and/or populate and look for '\0' characters
at read time.

Given what you're trying to do I would suggest you take a look at the
fgets function.

{
if(!isprint(buf fer[count]))
{
buffer[count] = '.';
}
else
{
fputc(buffer[count],outfile);
}

And this lot doesn't need to be in an else, it needs to happen every
time.

<snip rest of code>

[Ben Bacarisse]

Bill <bi*********@al lstate.comwrite s:

>>
You did not take my advice to trim your replies (you quoted everything
including my signature block). That will have won you no favours from
others here and it discourages me from helping further.

Sorry.

Well you get much credit for *not* digging in and arguing that your
way of posting is the right way. Thank you.

Yes it is an assignment, but I'm trying to take it further
than what was assigned.
I really wish to learn the language.

A simple solution, which will concentrate on the language features
rather than on getting the searching algorithm right, is to:

(1) Find out how big the file is. There are two ways to do this in
standard C, but only one that is guaranteed to work. If I were your
tutor I would accept both, provided your program reports any failures
as such.

(2) Allocate space for the whole file and read it in.

(3) Search for the string to replace whilst writing out those parts
that are not to be replaced.

There are obvious limitations with this strategy, but it will help you
learn. A fully general search and replace program is quite complex
for a beginner.

--
Ben.

[Bill]

There are obvious limitations with this strategy, but it will help you
learn. A fully general search and replace program is quite complex
for a beginner.

--
Ben.

Thanks for the tips.