How preprocessor works

**Albinoswordfish** · 04-10-2009

I thought I knew how the preprocessor worked until I ran until a recent problem.

Say I have the declaration below:

Code:

#define INFILE dataset

then later in my main function I have

Code:

FILE *fptr;
int p;
fptr = fopen("INFILE","r");
fscanf(fptr," %d",&p);

the file "dataset" exists with the number 5 in it.

However when I run this I get a segmentation fault. So I'm thinking the preprocessor doesn't replace INFILE with dataset which I thought it did.

Can anybody explain to me what's going on?

**quzah** · 04-10-2009

The preprocessor does not make substitutions from within strings.

Quzah.

**MK27** · 04-10-2009

I think you want

Code:

#define INFILE "dataset"
fptr = fopen(INFILE,"r");

Without the quotes, dataset would be considered to refer to another variable, eg

Code:

int mynum;
#define XXX mynum

Thread: How preprocessor works

Thread Tools

Search Thread

Display

How preprocessor works