sscanf is always a potential problem when converting numeric
values as it does not correctly handle over- and underflow
(or at least gives no indication that it has done so).

This change converts json_object_get_double() to use strtod()
according to CERT guidelines.

The -Bsymbolic-functions linker flag reduces the amount of PLT jumps in
a shared object, and has a side effect of preventing symbol collisions
in libraries and applications linking against two different shared
objects exposing the same symbol.

While the former is (generally) a performance win, the latter is less
rare than expected. For instance, PulseAudio started linking against
json-c a while ago; now, every project linking against PulseAudio is
leaking json-c symbols. In the GNOME platform, this means that projects
linking against PulseAudio cannot be safely linked against other
libraries depending on the GLib-based JSON parsing libraries JSON-GLib,
because of a symbol conflict. Nominally, this conflict would not be an
issue: libraries and applications do not need to depend on two different
JSON parsing libraries; the symbol leakage, though, ends up causing
either segmentation faults, or weird errors. For further reference,
please see: https://bugzilla.gnome.org/show_bug.cgi?id=703734

JSON-GLib already switched to using -Bsymbolic-functions, but it would
be safe if json-c did the same, wherever the linker flag is available.

Add json_object_free_userdata() and json_object_userdata_to_json_string() too.

Add const qualifiers to json_object_to_file and json_object_to_file_ext

Remove redefinition of strndup() which is no longer used in the codebase

Add extern to json_object_set_serializer so that it gets exported (Windows fix)

more strictness

fixing problem that isinf(-Inf) can be 1 or -1

Fix potential out-of-bounds read in json_tokener_error_desc

Found by Coverity. The number of elements of an array 'ar' is found by
sizeof(ar)/sizeof(ar[0]) and not sizeof(ar)

76const char *json_tokener_error_desc(enum json_tokener_error jerr)
 77{
 78        int jerr_int = (int)jerr;

1. Condition "jerr_int < 0", taking false branch

2. Condition "jerr_int > 112 /* (int)sizeof (gdal_json_tokener_errors) */", taking false branch
 79        if (jerr_int < 0 || jerr_int > (int)sizeof(json_tokener_errors))
 80                return "Unknown error, invalid json_tokener_error value passed to json_tokener_error_desc()";

CID 1076806 (#1 of 1): Out-of-bounds read (OVERRUN)3. overrun-local: Overrunning array "gdal_json_tokener_errors" of 14 8-byte elements at element index 112 (byte offset 896) using index "jerr" (which evaluates to 112).
 81        return json_tokener_errors[jerr];
 82}

filename should be passed as const char* to functions
json_object_to_file and json_object_to_file

Also adjust an error message in json_util to make it unique.  Fixes #87.

in strick mode, number must not start with 0

Support NaN and Infinity

Several MSVC fixes

Although JSON RFC does not support NaN or Infinity
as numeric values ECMA 262 section 9.8.1 defines
how to handle these cases as strings

int32_t is nowhere in msvc, so the version check could be even removed

one definition of json_object_object_foreach only works on c99 and later

Fix Broken Build, Check ADVANCE_CHAR

We forget to check or use the return value of the ADVANCE_CHAR macro,
and upon compilation an error is thrown because of its lack of use. This
patch checks to see if the macro was successful, and if not replaces the
offending character with a replacement.

While parsing token data, we use the POP_CHAR macro to 'peek' at
character data. This behaviour is noted in the comments for the macro,
yet the definition is left as 'pop'. Changing to PEEK_CHAR does not
imply that the character being observed is removed.

rename AM_CONFIG_HEADER to AC_CONFIG_HEADER