While scanf!=EOF or scanf==1?

Question

Ceteris paribus (well formed data, good buffering practices and what not), is there a reason why I prefer to loop while the return of scanf is 1, rather than !EOF? I may have read this somewhere, or whatever, but I may have it wrong as well. What do other people think?

Answer 1

scanf returns the number of items succesfully converted ... or EOF on error. So code the condition the way it makes sense.

scanfresult = scanf(...);
while (scanfresult != EOF) /* while scanf didn't error */
while (scanfresult == 1) /* while scanf performed 1 assignment */
while (scanfresult > 2) /* while scanf performed 3 or more assignments */

Contrived example

scanfresult = scanf("%d", &a);
/* type "forty two" */
if (scanfresult != EOF) /* not scanf error; runs, but `a` hasn't been assigned */;
if (scanfresult != 1) /* `a` hasn't been assigned */;

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Edit: added another more contrived example

int a[5], b[5];
printf("Enter up to 5 pairs of numbers\n");
scanfresult = scanf("%d%d%d%d%d%d%d%d%d%d", a+0,b+0,a+1,b+1,a+2,b+2,a+3,b+3,a+4,b+4);
switch (scanfresult) {
case EOF: assert(0 && "this didn't happen"); break;
case 1: case 3: case 5: case 7: case 9:
    printf("I said **pairs of numbers**\n");
    break;
case 0:
    printf("What am I supposed to do with no numbers?\n");
    break;
default:
    pairs = scanfresult / 2;
    dealwithpairs(a, b, pairs);
    break;
}

Answer 2

Depends what you want to do with malformed input - if your scan pattern isn't matched, you can get 0 returned. So if you handle that case outside the loop (for example if you treat it the same as an input error), then compare with 1 (or however many items there are in your scanf call).