关于 while(!EOF) 的问题

Question

Im reading in values from stdin and I want to keep reading the file until I have completed reading it all the way, so I am using

while(!EOF){ scanf(...) }

However, the code fragment doesn't seem to do anything,

while(!EOF){


    scanf("%d %d %d %d", &imageWidth, &imageHeight, &safeRegionStart, &safeRegionWidth);

    printf("---imageWidth=%d imageHeight=%d safeRegionStart=%d safeRegionWidth=%d---\n", imageWidth, imageHeight, safeRegionStart, safeRegionWidth);
    totalP = imageWidth * imageHeight ;
    totalSafeP = imageHeight * safeRegionWidth;


    printf("---total # of pixels: %d Total # of safe Pixels: %d---\n\n", totalP, totalSafeP);

    i=1;

    while(i!=totalP)
    {
        i++;
        scanf("%d", &pixel);
        printf("\nValue of pixel %d", pixel);


    }//End for scanning all pixels*/
}//while loop

EDIT: I fixed it

while(scanf("%d %d %d %d", &imageWidth, &imageHeight, &safeRegionStart, &safeRegionWidth)==4&&!feof(stdin)) { }

!feof(stdin) probably isn't necessary.

Answer 1

EOF is only an integer constant. On most systems it is -1 . !-1 is false and while(false) won't do anything.

What you want is to check the return values of scanf . scanf returns the number of successfully read items and eventually EOF .

Answer 2

Well, this is easy to answer:

EOF is a constant #define , eg #define EOF -1 .

So your while(!EOF) condition will always be false and the loop won't execute. You need to check the return value of scanf against EOF.

You need something like:

while(scanf("%d %d %d %d", &imageWidth, &imageHeight, &safeRegionStart, &safeRegionWidth) != EOF){

Answer 3

You have to use a variable to hold a char value that can be potentially EOF . Something like..

while(4==scanf("%d %d %d %d", &imageWidth, &imageHeight, &safeRegionStart, &safeRegionWidth)) {
//do stuff
}

Otherwise.EOF is always false.

Answer 4

The loop will never be entered. EOF is a constant value which is -1 (check stdio.h for this definition). So !EOF is 0 which is false, so it will never be entered.

To check that if the file has ended or not you can use: if (feof (file_ptr)) break;

while (1)
{
   /* Read file */
   if (feof (file_ptr))
     break;
   /* Do work */
}