Undeclared _snprintf for rapidjson?

Question

I'm getting the following error when attempting to build on CentOS 6.4: The only flags being passed here are -Wall and -std=c++11, using gcc 4.7.2

/usr/local/include/rapidjson/writer.h: In member function ‘void rapidjson::Writer::WriteDouble(double)’: /usr/local/include/rapidjson/writer.h:173:53: error: there are no arguments to ‘_snprintf’ that depend on a template parameter, so a declaration of ‘_snprintf’ must be available [-fpermissive] /usr/local/include/rapidjson/writer.h:173:53: note: (if you use ‘-fpermissive’, G++ will accept your code, but allowing the use of an undeclared name is deprecated)

The code in question: (from rapidjson/writer.h)

        void WriteDouble(double d) {
            char buffer[100];
#if _MSC_VER
            int ret = sprintf_s(buffer, sizeof(buffer), "%g", d);
#else
            int ret = snprintf(buffer, sizeof(buffer), "%g", d); //this line is the troublemaker
#endif
            RAPIDJSON_ASSERT(ret >= 1);
            for (int i = 0; i < ret; i++)
                    stream_.Put(buffer[i]);
    }

The top of the writer.h file looks like this:

#ifndef RAPIDJSON_WRITER_H_
#define RAPIDJSON_WRITER_H_

#include "rapidjson.h"
#include "internal/stack.h"
#include "internal/strfunc.h"
#include <cstdio>       // snprintf() or _sprintf_s()
#include <new>          // placement ne

Which led me to this question: cstdio stdio.h namespace.

As I understand the answer to the question above, the inclusion of cstdio should declare the snprintf symbol in the standard namespace. So, I thought to include stdio.h to get the symbol defined in the global namespace. The same compilation error results, regardless if I include cstdio, stdio.h, or both files (which I shouldn't have to do)

My question is two parts: Why is gcc looking for _snprintf and not snprintf? Or am I on the wrong track and is this related to the two-part name lookup that gcc does for template parameter binding? (ala 10.8.2, http://idlebox.net/2009/apidocs/gcc-4.4.1.zip/gcc-4.4.1/gcc_10.html#SEC315)

I was trying to get a declaration of _snprintf available, per the error message. I assumed (wrongly) that by including stdio.h, it would declare snprintf in the global namespace and that would resolve this problem. That turned out not to be the case, so the error remains. — jdt141
Just curious: did you unzip the sources inside /usr/local? — devnull
gcc version 4.7.2. The sources are in /usr/local/include/rapidjson. — jdt141

Jay Jay · Accepted Answer · 2013-04-04T18:06:59

Are you using the -ansi compile flag?

Using -ansi generally says that you want the headers to expose ONLY the interfaces mentioned in the C89 standard. But C89 did not describe snprintf

Undeclared _snprintf for rapidjson?

2 Answers