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Basic question on strings - please help!!

Hi I've a large data file made up as follows
5.537681 3.993655 -5.651005
1.835011 6.016797 -5.632307
-2.336837 5.943220 -5.699044
etc .....

Now I want to read in each line and based on the last number ie -5.651005, filter ( eg if > -5.6 move) the line to a new file.

I though about writing each line to a string and then trying to obtain -5.651005 within the string, but i wasnt sure how to do this.

Its a big original file, so it makes sence to read the line and filter it at the same time.

all advice gratefully received,
thanks, EG

ASKER CERTIFIED SOLUTION

garethwebbley

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ewest

You haven't stated (a) the underlying operating system and
(b) if the format of each line is well defined.

If you have a system w/ decent shell scripting capabilities, then you might want to forgo the C coding. On the other hand if C is /the/ way for you, then the coding will be greatly simplified if you can be certain that each line consists of the same set of data.

Simple case:
#include <stdio.h>

FILE * fpOrig;
FILE * fpNew;

double numA;
double numB;
double numC;
int rc;

fpOrig = fopen("thedatafile", "r");
fpNew = fopen("thenewfile", "w");

wroteNew = 0;

while (3 == (rc = fscanf(fpOrig, "%f %f %f",
&numA, &numB, &numC)))
{
if (numC > -5.6)
{
fprintf(fpNew, "%f %f %f",
&numA, &numB, &numC);
wroteNew++;
}
}

if (0 == wroteNew)
{
remove("thenewfile");
}
fclose(fpNew);
fclose(fpOrig);

Alternatively a combination of
fgets()
strtod()

can be used to apply better input error handling:

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

char line[80];
while (NULL != fgets(line, sizeof(line), fpOrig))
{
int i;
char * ptr;
char * endptr;
double dval;

/*
* trim off trailing newline
*/

/* get last numeric string, scan in reverse */
ptr = &line[strlen(line) - 1];
while (!isspace(ptr))
{
ptr--;
}

dval = strtod(ptr, &endptr);
if (endptr != ptr && dval > -5.6)
{
fputs(line, fpNew);
}
}

Note, this is untested, so I may have missed some closing parens. More importantly, little or no error checking is included.

sunnycoder

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