File I/O

[Yu-Loong Liew]

Hi all,

I have a question about file I/O. I am interested in processing a file with
unknown number of rows of data in the format of "xxx,xxx" to arrays. The
following code segment is what I have implemented. Any better way of doing
it?

int convert_data()
{
....

fstream = fopen (fileName, "r");
while (!feof(fstream))
{
fscanf (fstream, "%lf,%lf", &tempDouble, &tempDouble);
dataCount++;
}
rewind (fstream);
dataX = malloc (dataCount * sizeof(double));
dataY = malloc (dataCount * sizeof(double));

if (dataX == NULL || dataY == NULL)
{
printf("Unable to allocate memory!\n");
if (dataX != NULL) free (dataX);
if (dataY != NULL) free (dataY);
fclose(fstream);
exit(1);
}

for (idx = 0; idx < dataCount; idx++)
fscanf (fstream, "%lf, %lf", &dataX[idx], &dataY[idx]);

....
}

Thank you in advance!

Yu-Loong

 

[Artie Gold]

Hi all,

I have a question about file I/O. I am interested in processing a file with
unknown number of rows of data in the format of "xxx,xxx" to arrays. The
following code segment is what I have implemented. Any better way of doing
it?

int convert_data()
{
...

fstream = fopen (fileName, "r");

You need to see if the fopen() call succeeded.

while (!feof(fstream))

NO! Please see:

http://www.eskimo.com/~scs/C-faq/q12.2.html

(you *did* read the FAQ *first* didn't you?)

{
fscanf (fstream, "%lf,%lf", &tempDouble, &tempDouble);
dataCount++;
}
rewind (fstream);
dataX = malloc (dataCount * sizeof(double));
dataY = malloc (dataCount * sizeof(double));

if (dataX == NULL || dataY == NULL)
{
printf("Unable to allocate memory!\n");
if (dataX != NULL) free (dataX);
if (dataY != NULL) free (dataY);
fclose(fstream);
exit(1);
}

for (idx = 0; idx < dataCount; idx++)
fscanf (fstream, "%lf, %lf", &dataX[idx], &dataY[idx]);

...
}

Why read the file twice? If it's large, you'd be better off starting
your buffer(s) at some reasonable size and using realloc() to double the
size as needed (which would be O(log n) realloc()s).

Of course, if the file is small it doesn't matter much. ;-)

HTH,
--ag

 

[Allan Bruce]

Hi all,

I have a question about file I/O. I am interested in processing a file with
unknown number of rows of data in the format of "xxx,xxx" to arrays. The
following code segment is what I have implemented. Any better way of doing
it?

int convert_data()
{
...

fstream = fopen (fileName, "r");
while (!feof(fstream))
{
fscanf (fstream, "%lf,%lf", &tempDouble, &tempDouble);

be sure to check the return value of fscanf to see if it has assigned the
correct number of arguements.
Allan

 

[Yu-Loong Liew]

Sorry, I didn't read the FAQ.

Thanks for your help.

Yu-Loong

Hi all,

I have a question about file I/O. I am interested in processing a file with
unknown number of rows of data in the format of "xxx,xxx" to arrays. The
following code segment is what I have implemented. Any better way of doing
it?

int convert_data()
{
...

fstream = fopen (fileName, "r");

You need to see if the fopen() call succeeded.

while (!feof(fstream))

NO! Please see:

http://www.eskimo.com/~scs/C-faq/q12.2.html

(you *did* read the FAQ *first* didn't you?)

{
fscanf (fstream, "%lf,%lf", &tempDouble, &tempDouble);
dataCount++;
}
rewind (fstream);
dataX = malloc (dataCount * sizeof(double));
dataY = malloc (dataCount * sizeof(double));

if (dataX == NULL || dataY == NULL)
{
printf("Unable to allocate memory!\n");
if (dataX != NULL) free (dataX);
if (dataY != NULL) free (dataY);
fclose(fstream);
exit(1);
}

for (idx = 0; idx < dataCount; idx++)
fscanf (fstream, "%lf, %lf", &dataX[idx], &dataY[idx]);

...
}

Why read the file twice? If it's large, you'd be better off starting
your buffer(s) at some reasonable size and using realloc() to double the
size as needed (which would be O(log n) realloc()s).

Of course, if the file is small it doesn't matter much. ;-)

HTH,
--ag