Greetings,

I am trying to write a data file using a native C structure which has floats in it. Is this possible? My system is Windows XP with Visual C 6, and ActiveState perl. I am not trying to cross platforms, I just want to transfer from perl float to c float directly into a structure format. I could translate from a text file to the structure in c, but would rather do it in perl.

Enclosed are some sample code. I have tried pack with with "f" and "d", but end up with garbage in the structure.

 
#write test file
open OUTF, ">c\\current\\test.bin";
binmode (OUTF);

my $buff = pack "sfff", 99, 1.34, 1.44, 1.55;
print OUTF $buff;
print OUTF $buff;

close OUTF;
print "done.\n";

[download]
 
// test reader in visual c 6
typedef struct
{
    short  ss;
    float  a,b,c;
}
TEST_REC;


void iitest()
{
    FILE    *fd;
    TEST_REC  tester[2];
    long rv;

    fd = fopen("test.bin","r");
        
    rv = fread( tester, sizeof(TEST_REC), 2, fd);
       
    printf(" ss %d, %5.3f, %5.3f, %5.3f, \n", tester[0].ss, tester[0].
+a,tester[0].b,tester[0].c);
    printf(" ss %d, %5.3f, %5.3f, %5.3f, \n", tester[1].ss, tester[1].
+a,tester[1].b,tester[1].c);
    
    fclose(fd);
    exit (0);
}

[download]

Thanks. Eugene

UPDATE

The padding was the problem on the c side structure (padded to 4 bytes). I was already dealing with the padding elsewhere, but didn't think about it here. DUH! I was too focused on thinking the float was the problem.

I added the short as a sanity check, but since I was already insane...

Thanks.

In reply to transfer float data to c by NatureFocus

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