fscanf return value

Question

What does fscanf return when it reads data in the file. For example,

int number1, number2, number3, number4, c;

c = fscanf (spFile, "%d", &number1);
//c will be 1 in this case.

c = fscanf (spFile, "%d %d %d %d", &number1, &number1, &number3, &number4);
//in this case, c will return 4.

I just want to know why it returns such values depending on the number of arguments.

Answer 1

From the manpage for the Xscanf family of functions:

Upon successful completion, these functions shall return the number of successfully matched and assigned input items; this number can be zero in the event of an early matching failure. If the input ends before the first matching failure or conversion, EOF shall be returned. If a read error occurs, the error indicator for the stream is set, EOF shall be returned, and errno shall be set to indicate the error

So your first call to fscanf returns 1 because one input item (&number1) was successfully matched with the format specifier %d. Your second call to fscanf returns 4 because all 4 arguments were matched.

Answer 2

I quote from cplusplus.com .

On success, the function returns the number of items of the argument list successfully filled. This count can match the expected number of items or be less (even zero) due to a matching failure, a reading error, or the reach of the end-of-file.

If a reading error happens or the end-of-file is reached while reading, the proper indicator is set (feof or ferror). And, if either happens before any data could be successfully read, EOF is returned.

--EDIT--

If you are intention is to determine the number of bytes read to a string.

int bytes;
char str[80];
fscanf (stdin, "%s%n",str,&bytes);
printf("Number of bytes read = %d",bytes);