C help: how do I use a string to specify a filename?

[KrazyHorse]

I'm going to be outputting data to a bunch of different files with slightly different names.

The output filename should be of the form

/home/mmcevoy/3year/princcomp/ver2/tempnumber.dat

where number is an integer I'm pulling out of a list (and temp stays as a literal part of filename)

so, first I define the C-string

char dat[] = ".dat\"";

then I define my list of numbers as list

I set i to a specific integer and test by assigning

char tfilename[200];
sprintf(tfilename, "\"/home/mmcevoy/3year/princcomp/ver2/temp%d%s", list[i], dat);

when I do

printf("%s", tfilename);

the output reads

"/home/mmcevoy/3year/princcomp/ver2/temp1238.dat" (1238 is the right number)

but when I do

FILE *filet;
filet = fopen(tfilename, "w");
fclose(filet);

it compiles, but I get a segfault when I attempt to run

(using gcc compiler)

[VetLegion]

Check whether you have write permission on the destination folder.

[VetLegion]

Actually, I think you have extra quotation marks in the string (they shouldn't be there).

[KrazyHorse]

a) I do have write permission to that folder

b) If I don't need quote marks then why do I need quote marks when I manually specify the filename?

I can't test right now since I'm back home. Actually, I could, but I don't feel like sshing in to my account.

[VetLegion]

Does

printf("%s", tfilename);

output

"/home/mmcevoy/3year/princcomp/ver2/temp1238.dat"

or

/home/mmcevoy/3year/princcomp/ver2/temp1238.dat

If it's the former, fopen() will throw an error since it expects the filename without the quotation marks.

When you

fopen( "somefile.dat", "w" );

you actually pass the filename without the quotation marks, they simply delineate the string from the rest of the code.

[VetLegion]

Anyway, I'm not 100% sure since I haven't written any C code in about five years, but it doesn't cost you anything to try

[KrazyHorse]

it prints the first one

what I don't get is that if I wanted to manually type in the filename I would have to write

FILE *filet;
filet = fopen("/home/mmcevoy/3year/princcomp/ver2/temp1238.dat", "w");
fclose(filet);

but when I input the filename as a string the string does not need quote marks

I'm not the greatest programmer in the world, so if there's an obvious reason that's probably what I'm not getting

[Kuciwalker]

Because the quote marks in the manually entered filename are what make it a string. The actually string passed to the function doesn't include quote marks.

[KrazyHorse]

are the double quote marks somehow the method that the fopen function uses to parse the typing into a string, therefore if it's already a string it doesn't need them?

EDIT: I guess so. Thanks, guys

[Whoha]

Re: C help: how do I use a string to specify a filename?

try // instead of /

also, this is unix so you probably need to do something like ./filename

[KrazyHorse]

a) / is not a reserved symbol; \ is

b) I'm pretty sure vetlegion and kuci already explained the answer

[KrazyHorse]

Re: Re: C help: how do I use a string to specify a filename?

Originally posted by Whoha
also, this is unix so you probably need to do something like ./filename

No, I don't

I'm not asking it to force to current directory; I'm asking it to write to the same directory no matter where I run program from in my home

[Whoha]

you've got it all right, disregard what I said.

[KrazyHorse]

Thanks, though

[Whoha]

Why are you using sprintf? I've always been able to just initialize such strings.