CODEWITHSUNDEEP
cwarningsimplicit-declaration
Bob
Bob

Reputation: 735

dprintf implicit declaration warning

When using dprintf() I'm getting the warning "implicit declaration of dprintf". That tends to mean a necessary file isn't included, but I already included stdio.h, which is supposed to be all that it needs. Is there something else dprintf needs?

Upvotes: 3

Views: 2929

Answers (3)

NUTTAPAT KOONARANGSRI
NUTTAPAT KOONARANGSRI

Reputation: 31

You can look up for fprintf() here.

I ran into the same problem and hence I was forced to run on POSIX based machine, I must changed my code, so fprintf() is one of (may be) many options I had. example :

fprintf(stderr,"file not found");

Upvotes: 0

Ken Keys
Ken Keys

Reputation: 236

The "feature_test_macros" section of the man page explains that to make stdio.h declare dprintf(), you must first #define _POSIX_C_SOURCE 200809L (or higher) before you #include <stdio.h>. The reason for this is that dprintf() was not standardized until POSIX.1-2008, but <stdio.h> needs to continue to work with code written before that, even if that code used its own identifier named "dprintf". (Defining _GNU_SOURCE or _XOPEN_SOURCE would also work on Linux, but _POSIX_C_SOURCE is the best choice for general portability.)

Upvotes: 3

deamentiaemundi
deamentiaemundi

Reputation: 5525

You might need to set some macros. Put on top of the file, before any includes the following

#define _POSIX_C_SOURCE  200809L
#define _GNU_SOURCE

(One of that would be enough but I don't know the GLibC version you use)

Upvotes: 2

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