Reading a file...

[EdUarDo]

Hi all, I'm not a newbie with C, but I don't use it since more than 5 years...

I'm trying to read a text file which has doubles in it:

1.0 1.1 1.2 1.3 1.4
2.0 2.1 2.2 2.3 2.4
I'm doing this (it's only a test trying to achieve the goal...):

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

int main () {
FILE* pFile;
long lSize;
double* buffer;

pFile = fopen ( "fichero_test.t xt" , "r" );
if (pFile==NULL) exit (1);

// obtain file size.
fseek (pFile , 0 , SEEK_END);
lSize = ftell (pFile);
rewind (pFile);

// allocate memory to contain the whole file.
buffer = (double*) malloc (lSize);
if (buffer == NULL) exit (2);

// copy the file into the buffer.
fread (buffer,1,lSize ,pFile);
printf("Pos 2 - %lf\n", buffer[2]);
printf("Pos 2 - %lf\n", buffer[sizeof(double)* 2]);

// terminate
fclose (pFile);
free (buffer);
return 0;
}

The output is:

Pos 2 - 0.000000
Pos 2 - 0.000000

What am I doing wrong?, Can I read the whole file into a buffer?

[Nick Keighley]

EdUarDo wrote:

Hi all, I'm not a newbie with C, but I don't use it since more than 5 years...
you have some severe misconceptions about how C i/o works. I recomend
you get yourself a good book (eg K&R) which will explain things
clearly.
I'm trying to read a text file which has doubles in it:

1.0 1.1 1.2 1.3 1.4
2.0 2.1 2.2 2.3 2.4
to be honest the simplest method is something like:-

void read_line (double dd [5], FILE *f)
{
if (fscanf(f, "%lf %lf %lf %lf %lf", &dd[0], &dd[1], &dd[2],
&dd[3], &dd[4)
!= 5)
{
exit (EXIT_FAILURE);
}
}

code is untested, uncompiled etc.
I'm doing this (it's only a test trying to achieve the goal...):

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

int main () {
int main (void)

is better style
FILE* pFile;
long lSize;
double* buffer;

pFile = fopen ( "fichero_test.t xt" , "r" );
if (pFile==NULL) exit (1);
error checking, good!

// obtain file size.
fseek (pFile , 0 , SEEK_END);
lSize = ftell (pFile);
rewind (pFile);
I'm not certain this works on a text file...

// allocate memory to contain the whole file.
buffer = (double*) malloc (lSize);
don't cast malloc()
if (buffer == NULL) exit (2);

// copy the file into the buffer.
fread (buffer,1,lSize ,pFile);
printf("Pos 2 - %lf\n", buffer[2]);
so you've read about 40 characters into a buffer. Why do you expect to
find and doubles in the buffer? In ascii that's something like

31 2E 30 20 31 2E 31 etc.

(yes I know it doesn't have to be ascii but I thought this made the
point
better than '1' '.' '0' ' ' '1' '.' '1' etc. you disagree?)

You can't jsut stuff characters into a buffer and expect sane results.
printf("Pos 2 - %lf\n", buffer[sizeof(double)* 2]);
// terminate
fclose (pFile);
free (buffer);
return 0;
}

The output is:

Pos 2 - 0.000000
Pos 2 - 0.000000

What am I doing wrong?, Can I read the whole file into a buffer?

yes, but you have to convert from characters to double. The best
combination is fgets() to read a line followed by sscanf() to parse the
line.
Always check the return value of sscanf().

--
Nick Keighley

[EdUarDo]

> you have some severe misconceptions about how C i/o works. I recomend

you get yourself a good book (eg K&R) which will explain things
clearly.
Sure, now I'm used to other languages and indeed I don't remember anything about C I/O

1.0 1.1 1.2 1.3 1.4
2.0 2.1 2.2 2.3 2.4

void read_line (double dd [5], FILE *f)
{
if (fscanf(f, "%lf %lf %lf %lf %lf", &dd[0], &dd[1], &dd[2],
&dd[3], &dd[4)
!= 5)
{
exit (EXIT_FAILURE);
}
}

Well, it doesn't works for me because the real file could have 5, 6 or 1000 items per line.

// obtain file size.
fseek (pFile , 0 , SEEK_END);
lSize = ftell (pFile);
rewind (pFile);

I'm not certain this works on a text file...

It does...

// allocate memory to contain the whole file.
buffer = (double*) malloc (lSize);

don't cast malloc()

ok
You can't jsut stuff characters into a buffer and expect sane results.
Yeah, I guess that, but I wasn't sure of it, that's the reason I've asked for help....
yes, but you have to convert from characters to double. The best
combination is fgets() to read a line followed by sscanf() to parse the
line.
I suppose there isn't a readLine function, so I'll need to read until I reach a '\n' character, isn't it?
Always check the return value of sscanf().

[pemo]

EdUarDo wrote:

Hi all, I'm not a newbie with C, but I don't use it since more than 5
years...
I'm trying to read a text file which has doubles in it:

1.0 1.1 1.2 1.3 1.4
2.0 2.1 2.2 2.3 2.4
I'm doing this (it's only a test trying to achieve the goal...):

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

int main () {
FILE* pFile;
long lSize;
double* buffer;

pFile = fopen ( "fichero_test.t xt" , "r" );
if (pFile==NULL) exit (1);

// obtain file size.
fseek (pFile , 0 , SEEK_END);
lSize = ftell (pFile);
rewind (pFile);

// allocate memory to contain the whole file.
buffer = (double*) malloc (lSize);
if (buffer == NULL) exit (2);

// copy the file into the buffer.
fread (buffer,1,lSize ,pFile);
printf("Pos 2 - %lf\n", buffer[2]);
printf("Pos 2 - %lf\n", buffer[sizeof(double)* 2]);

// terminate
fclose (pFile);
free (buffer);
return 0;
}

The output is:

Pos 2 - 0.000000
Pos 2 - 0.000000

What am I doing wrong?, Can I read the whole file into a buffer?

Does this thread on 'c file reading' help?

http://groups.google.com/group/comp....41f9f1ba8ac3d9
--
==============
Not a pedant
==============

[EdUarDo]

> Does this thread on 'c file reading' help?

Yes, thanks.

[santosh]

EdUarDo wrote:

Hi all, I'm not a newbie with C, but I don't use it since more than 5 years...

I'm trying to read a text file which has doubles in it:

1.0 1.1 1.2 1.3 1.4
2.0 2.1 2.2 2.3 2.4
I'm doing this (it's only a test trying to achieve the goal...):

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

int main () { FILE* pFile;
long lSize;
double* buffer;

pFile = fopen ( "fichero_test.t xt" , "r" );
if (pFile==NULL) exit (1);

exit(EXIT_FAILU RE) or return EXIT_FAILURE might be more portable.
// obtain file size.
Same for the comment syntax.
fseek (pFile , 0 , SEEK_END);
lSize = ftell (pFile);
rewind (pFile);
I don't know how well this will work. Unless your file is very large,
why not calculate it's size by reading each byte till EOF?
// allocate memory to contain the whole file.
buffer = (double*) malloc (lSize);
The cast is unnecessary and might hide the failure to include stdlib.h,
which on some systems might result in the compiler using the wrong
value as the return from malloc().
if (buffer == NULL) exit (2);
See comment about exit().
// copy the file into the buffer.
fread (buffer,1,lSize ,pFile);
printf("Pos 2 - %lf\n", buffer[2]);
printf("Pos 2 - %lf\n", buffer[sizeof(double)* 2]);
Here's your problem. The values read from the file will be present as
characters in memory. But you supply a conversion specifier doubles.
You'll need to convert the values using possibly sscanf() or strtod()
and then display them.
What am I doing wrong?, Can I read the whole file into a buffer?

If you allocated the required memory, then yes, you can.

[John Bode]

Since my last reply apparently got lost in the aether...

EdUarDo wrote:

Hi all, I'm not a newbie with C, but I don't use it since more than 5 years...

I'm trying to read a text file which has doubles in it:

1.0 1.1 1.2 1.3 1.4
2.0 2.1 2.2 2.3 2.4
I'm doing this (it's only a test trying to achieve the goal...):

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

int main () {
FILE* pFile;
long lSize;
double* buffer;

pFile = fopen ( "fichero_test.t xt" , "r" );
if (pFile==NULL) exit (1);

// obtain file size.
fseek (pFile , 0 , SEEK_END);
lSize = ftell (pFile);
rewind (pFile);

// allocate memory to contain the whole file.
buffer = (double*) malloc (lSize);
Unless you're using a pre-C89 compiler (or C++), don't cast the result
of malloc. You don't need to, and doing so can mask an error if you
forget to include stdlib.h.
if (buffer == NULL) exit (2);

Okay, first problem: the size of the file does not correspond to the
number of double values represented in that file. You have 10 strings
representing double values taking up (at least) 40 bytes. So sizing
your buffer based on the number of bytes in the file isn't going to do
what you want.

You're better off by allocating a small buffer and extending it with
realloc() as you read from the file. Granted, storing the contents of
an entire file in memory isn't terribly scalable whether you allocate
the memory in one huge gulp or in smaller chunks, but at least this way
you'll be allocating the right amount.
// copy the file into the buffer.
fread (buffer,1,lSize ,pFile);
Second problem: fread() does not convert the text representation of a
double value ("1.23") to the equivalent value (1.23). Basically what
you're doing is interpreting the bytes for "1.0 1.1 1.2..." as a series
of doubles, which is going to give you gibberish.
printf("Pos 2 - %lf\n", buffer[2]);
printf("Pos 2 - %lf\n", buffer[sizeof(double)* 2]);

// terminate
fclose (pFile);
free (buffer);
return 0;
}

The output is:

Pos 2 - 0.000000
Pos 2 - 0.000000

What am I doing wrong?, Can I read the whole file into a buffer?

Here's how I'd write it (uncompiled, untested, all the usual caveats
apply):

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

#define BASE 10
#define EXTENT 5

int main(void)
{
double *buffer = NULL;
file *pFile = NULL;
size_t curSize = BASE;
size_t index = 0;
int moreData = 1;

if ((pFile = fopen("fichero_ test.txt", "r")) == NULL)
{
fprintf(stderr, "Could not open fichero_test.tx t!\n");
return EXIT_FAILURE;
}

/*
* Allocate the buffer at its initial size.
*/
buffer = malloc(sizeof *buffer * curSize);
if (!buffer)
{
fprintf(stderr, "Could not allocate initial buffer!\n");
return EXIT_FAILURE;
}

while (moreData)
{
/*
* Extend the buffer as necessary.
*/
if (index == curSize)
{
double *tmp = realloc(buffer, sizeof *buffer * (curSize +
EXTENT));
if (tmp)
{
buffer = tmp;
curSize += EXTENT;
}
else
{
fprintf(stderr, "Could not extend buffer past %lu
bytes; exiting...\n", curSize);
free(buffer);
return EXIT_FAILURE;
}
}

/*
* To keep this example simple, we're going to assume
* that the input file is *always* well-formatted, and
* that we don't have to handle any malformed
* strings.
*/
if (fscanf(pFile, "%f", &buffer[index++]) == 0)
{
/*
* Previous read failed; either we hit
* EOF or there was an error. Either
* way we're going to break out of the loop.
*/
if (feof(pFile))
{
fprintf(stderr, "Hit end-of-file...exiting loop\n");
}
else
{
fprintf(stderr, "Error reading from file...exiting
loop\n");
}
moreData = 0;
}
}

fprintf(stdout, "Read %lu doubles from input file.\n", index+1);
fprintf(stdout, "buffer[%lu] = %f\n", index, buffer[index]);

free(buffer);
fclose(pFile);

return EXIT_SUCCESS;
}

[Fred Kleinschmidt]

"EdUarDo" <ed************ *****@NOSPAMgma il.com> wrote in message
news:48******** ****@individual .net...

Hi all, I'm not a newbie with C, but I don't use it since more than 5
years...

I'm trying to read a text file which has doubles in it:

1.0 1.1 1.2 1.3 1.4
2.0 2.1 2.2 2.3 2.4
I'm doing this (it's only a test trying to achieve the goal...):

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

int main () {
FILE* pFile;
long lSize;
double* buffer;

pFile = fopen ( "fichero_test.t xt" , "r" );
if (pFile==NULL) exit (1);

// obtain file size.
fseek (pFile , 0 , SEEK_END);
lSize = ftell (pFile);
rewind (pFile);

// allocate memory to contain the whole file.
buffer = (double*) malloc (lSize); Don't cast malloc!

lSize is now set to the number of characters in the file.
What does this have to do with the number of values that represent real
numbers?
(Answer: nothing, other than a upper limit to the possible number of values)

if (buffer == NULL) exit (2);

// copy the file into the buffer.
fread (buffer,1,lSize ,pFile);
Why are yoiu using fread? fread is for reading binary data.
You have already stated that the file is text.
printf("Pos 2 - %lf\n", buffer[2]);
printf("Pos 2 - %lf\n", buffer[sizeof(double)* 2]);

// terminate
fclose (pFile);
free (buffer);
return 0;
}

The output is:

Pos 2 - 0.000000
Pos 2 - 0.000000

What am I doing wrong?, Can I read the whole file into a buffer?

If the number of values per line is not relevant and all you want to do is
just read all of the double values, you could just loop
forever using fscanf() until you get EOF. Your buffer is guaranteed
to be large enough (way too large, as a matter of fact).

A better way might be to start with a small buffer, read until it is
full, then realloc it by some increment, keeping track of the current size
and the current number of items reads.

--
Fred L. Kleinschmidt
Boeing Associate Technical Fellow
Technical Architect, Software Reuse Project

[santosh]

John Bode wrote:

Since my last reply apparently got lost in the aether...

EdUarDo wrote:

Hi all, I'm not a newbie with C, but I don't use it since more than 5 years...

I'm trying to read a text file which has doubles in it:

1.0 1.1 1.2 1.3 1.4
2.0 2.1 2.2 2.3 2.4

Here's how I'd write it (uncompiled, untested, all the usual caveats
apply):

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

#define BASE 10
#define EXTENT 5

int main(void)
{
double *buffer = NULL;
file *pFile = NULL;
size_t curSize = BASE;
size_t index = 0;
int moreData = 1;

if ((pFile = fopen("fichero_ test.txt", "r")) == NULL)
{
fprintf(stderr, "Could not open fichero_test.tx t!\n");
return EXIT_FAILURE;
}

/*
* Allocate the buffer at its initial size.
*/
buffer = malloc(sizeof *buffer * curSize);
if (!buffer)
{
fprintf(stderr, "Could not allocate initial buffer!\n");
return EXIT_FAILURE;
}

while (moreData)
{
/*
* Extend the buffer as necessary.
*/
if (index == curSize)
{
double *tmp = realloc(buffer, sizeof *buffer * (curSize +
EXTENT));
if (tmp)
{
buffer = tmp;
curSize += EXTENT;
}
else
{
fprintf(stderr, "Could not extend buffer past %lu
bytes; exiting...\n", curSize);
free(buffer);
return EXIT_FAILURE;
}
}

/*
* To keep this example simple, we're going to assume
* that the input file is *always* well-formatted, and
* that we don't have to handle any malformed
* strings.
*/
if (fscanf(pFile, "%f", &buffer[index++]) == 0)
{
/*
* Previous read failed; either we hit
* EOF or there was an error. Either
* way we're going to break out of the loop.
*/
if (feof(pFile))
{
fprintf(stderr, "Hit end-of-file...exiting loop\n");
}
else
{
fprintf(stderr, "Error reading from file...exiting
loop\n");
}
moreData = 0;
}
}

fprintf(stdout, "Read %lu doubles from input file.\n", index+1);
fprintf(stdout, "buffer[%lu] = %f\n", index, buffer[index]);

free(buffer);
fclose(pFile);

return EXIT_SUCCESS;
}

D:\Files\src\C\ tmp\fischero>gc c -Wall -ansi -pedantic -o fichero.exe
fichero.c
fichero.c: In function `main':
fichero.c:47: warning: long unsigned int format, size_t arg (arg 3)
fichero.c:59: warning: float format, double arg (arg 3)
fichero.c:78: warning: long unsigned int format, size_t arg (arg 3)
fichero.c:79: warning: long unsigned int format, size_t arg (arg 3)

Running the output, fichero.exe just hangs with 100% CPU usage, until
it's killed with CTRL-C.

[santosh]

John Bode wrote:

Since my last reply apparently got lost in the aether...
Here's how I'd write it (uncompiled, untested, all the usual caveats
apply):

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

#define BASE 10
#define EXTENT 5

int main(void)
{
double *buffer = NULL;
file *pFile = NULL;
size_t curSize = BASE;
size_t index = 0;
int moreData = 1;

if ((pFile = fopen("fichero_ test.txt", "r")) == NULL)
{
fprintf(stderr, "Could not open fichero_test.tx t!\n");
return EXIT_FAILURE;
}

/*
* Allocate the buffer at its initial size.
*/
buffer = malloc(sizeof *buffer * curSize);
if (!buffer)
{
fprintf(stderr, "Could not allocate initial buffer!\n");
return EXIT_FAILURE;
}

while (moreData)
{
/*
* Extend the buffer as necessary.
*/
if (index == curSize)
{
double *tmp = realloc(buffer, sizeof *buffer * (curSize +
EXTENT));
if (tmp)
{
buffer = tmp;
curSize += EXTENT;
}
else
{
fprintf(stderr, "Could not extend buffer past %lu
bytes; exiting...\n", curSize);
free(buffer);
return EXIT_FAILURE;
}
}

/*
* To keep this example simple, we're going to assume
* that the input file is *always* well-formatted, and
* that we don't have to handle any malformed
* strings.
*/
if (fscanf(pFile, "%f", &buffer[index++]) == 0)
What if EOF is returned? Better to store the return value into a
temporary and check against both zero and EOF. I did that and it fixed
the infinite loop hang mentioned in the previous post.
{
/*
* Previous read failed; either we hit
* EOF or there was an error. Either
* way we're going to break out of the loop.
*/
if (feof(pFile))
{
fprintf(stderr, "Hit end-of-file...exiting loop\n");
}
else
{
fprintf(stderr, "Error reading from file...exiting
loop\n");
}
moreData = 0;
}
}

fprintf(stdout, "Read %lu doubles from input file.\n", index+1);
fprintf(stdout, "buffer[%lu] = %f\n", index, buffer[index]);

Both these fprintf() statements print the wrong values, even if an
empty file is given.
I think the problem lies in the use of the variable 'index'.