How does fprintf in c++ work?

Question

how does fprintf works??

if i write fprintf(outfile, "test %d %d 255/r", 255, 255);

what does it mean?? i know outfile, is the name my of output file. what would the other values mean?

Answer 1

"test %d %d 255/r" tells that after it will be arguments (and they are there: 255, 255) and they are expected to be of integer type. And they will be placed instead of %d.

In result you'll get string test 255 255 255 in your file.

For more infrormation read fprintf reference.

Answer 2

It's similar to printf, it just prints the output to a file.

Answer 3

The first parameter is a file handle, the second is a formatting string, and after that there is a variable number of arguments depending on how many format specifiers you used in your 2nd parameter.

Check the documentation, it contains all of the information you are asking.

Answer 4

The second argument is the format string. Any additional arguments are the parameters to the specifier in the format string (in this case, %d). Check out http://www.cppreference.com/wiki/c/io/printf for a good intro to printf-style functions.

Answer 5

it's a formatted output to a file stream. It works like printf does, the difference is that printf always outputs to stdout.If you wrote

fprintf(stdout, "test %d %d 255\n", 255, 255);

it would be the same as the printf equivalent.

The second argument to it is the format string. The format string contains format specifiers, like %s, %d, %x. Yours contains two %ds. Each format specifier must have a corresponding argument in fprintf. Yours has two %d specifiers, so there are two numerical arguments:

fprintf(outfile, "Here are two numbers: %d, %d", 4, 5);

likewise, you could use string specifiers (%s), hexadecimal specifiers (%x) or long/long long int specifiers (%ld, %lld). Here is a list of them: http://www.cppreference.com/wiki/c/io/printf. Note that they are the same for all of the C formatted i/o functions (like sprintf and scanf).

Also, in your original example, "/r" will just literally print "/r". It looks like you were trying to do a carriage return ("\r").