Docs: First pass to update README.developer to C11

Update to reflect the transition from C99 to C11. Remove obsolete
comments and recommendations. Add a bit about transitioning to C
fixed width types.

Related to #17768.

doc/README.developer

@@ -65,39 +65,38 @@ Wireshark runs on many platforms, and can be compiled with a number of
 different compilers; here are some rules for writing code that will work
 on multiple platforms.
 
-In general, not all C99 features can be used since some C compilers used to
-compile Wireshark, such as Microsoft's C compiler, don't support all C99
-features.  The C99 features that can be used are:
+Building Wireshark requires a compiler that supports C11. This includes
+reasonably recent version of GCC and clang. Microsoft Visual Studio supports
+C11 from Visual Studio 2019 version 16.8 and later. Support requires an updated
+Universal C Runtime (UCRT) and Windows SDK version to work properly with the
+conforming preprocessor. The minimum SDK version is 10.0.20348.0 (version 2104).
 
- - flexible array members
- - compound literals
- - designated initializers
- - "//" comments
- - mixed declarations and code
- - new block scopes for selection and iteration statements (that is, declaring
-   the type in a for-loop like: for (int i = 0; i < n; i++) ;)
- - macros with a variable number of arguments (variadic macros)
- - trailing comma in enum declarations
- - inline functions (guaranteed only by use of glib.h)
+The C11 has some optional parts that are not a requirement to build Wireshark.
+In particular the following optional C11 features must NOT be used:
+ - Variable length arrays
+ - Bounds-checking interfaces (Annex K)
+
+We don't allow them because their value is questionable and requiring them
+would exclude a lot of compilers and runtimes that we wish to support.
 
 Don't initialize global or static variables (variables with static
-storage duration) in their declaration with non-constant values.  Not
-all compilers support this.  E.g., if "i" is a static or global
+storage duration) in their declaration with non-constant values. This is not
+permitted in C.  E.g., if "i" is a static or global
 variable, don't declare "i" as
 
-    guint32 i = somearray[2];
+    uint32_t i = somearray[2];
 
 outside a function, or as
 
-    static guint32 i = somearray[2];
+    static uint32_t i = somearray[2];
 
 inside or outside a function, declare it as just
 
-    guint32 i;
+    uint32_t i;
 
 or
 
-    static guint32 i;
+    static uint32_t i;
 
 and later, in code, initialize it with
 
@@ -107,34 +106,27 @@ instead.  Initializations of variables with automatic storage duration -
 i.e., local variables - with non-constant values is permitted, so,
 within a function
 
-    guint32 i = somearray[2];
+    uint32_t i = somearray[2];
 
 is allowed.
 
 Don't use zero-length arrays as structure members, use flexible array members
 instead.
 
-Don't use anonymous unions; not all compilers support them.
-Example:
-
-    typedef struct foo {
-      guint32 foo;
-      union {
-        guint32 foo_l;
-        guint16 foo_s;
-      } u;  /* have a name here */
-    } foo_t;
-
 Don't use "uchar", "u_char", "ushort", "u_short", "uint", "u_int",
 "ulong", "u_long" or "boolean"; they aren't defined on all platforms.
-If you want an 8-bit unsigned quantity, use "guint8"; if you want an
+Use the fixed width integers provided in C since C99. These are defined
+in <stdint.h>.
+
+If you want an 8-bit unsigned quantity, use "uint8_t"; if you want an
 8-bit character value with the 8th bit not interpreted as a sign bit,
-use "guchar"; if you want a 16-bit unsigned quantity, use "guint16";
-if you want a 32-bit unsigned quantity, use "guint32"; and if you want
-an "int-sized" unsigned quantity, use "guint"; if you want a boolean,
-use "gboolean".  Use "%d", "%u", "%x", and "%o" to print those types;
-don't use "%ld", "%lu", "%lx", or "%lo", as longs are 64 bits long on
-many platforms, but "guint32" is 32 bits long.
+use "unsigned char"; if you want a 16-bit unsigned quantity, use "uint16_t";
+if you want a 32-bit unsigned quantity, use "uint32_t"; and if you want
+an "int-sized" unsigned quantity, use "unsigned"; if you want a boolean,
+use "bool" (defined in <stdbool.h>). You don't need to explicitly include
+these headers; they are included in <wireshark.h>. Use that instead.
+
+To print fixed width integers you MUST use the macros provided in <inttypes.h>.
 
 Don't use "long" to mean "signed 32-bit integer", and don't use
 "unsigned long" to mean "unsigned 32-bit integer"; "long"s are 64 bits
@@ -144,7 +136,7 @@ long on many platforms.  Use "gint32" for signed 32-bit integers and use
 Don't use "long" to mean "signed 64-bit integer" and don't use "unsigned
 long" to mean "unsigned 64-bit integer"; "long"s are 32 bits long on
 many other platforms.  Don't use "long long" or "unsigned long long",
-either, as not all platforms support them; use "gint64" or "guint64",
+either, as not all platforms support them; use "int64_t" or "uint64_t",
 which will be defined as the appropriate types for 64-bit signed and
 unsigned integers.
 
@@ -170,23 +162,29 @@ will have to cast to a compatible data type, e.g.
 
     size_t i;
     char greeting[] = "hello, sailor";
-    guint byte_after_greet;
+    uint8_t byte_after_greet;
 
     i = strlen(greeting);
-    byte_after_greet = tvb_get_guint8(tvb, (gint) i); /* OK */
+    byte_after_greet = tvb_get_guint8(tvb, (int) i); /* OK */
 
 or
 
-    gint i;
+    int i;
     char greeting[] = "hello, sailor";
-    guint byte_after_greet;
+    uint8_t byte_after_greet;
 
-    i = (gint) strlen(greeting);
+    i = (int) strlen(greeting);
     byte_after_greet = tvb_get_guint8(tvb, i); /* OK */
 
 See http://www.unix.org/version2/whatsnew/lp64_wp.html for more
 information on the sizes of common types in different data models.
 
+A lot of legacy code still uses GLib types and I/O replacement API. These
+should be gradually transitioned to use the standard interfaces provided in
+C11. Sometimes it may be necessary to use an unsavory cast or two or abuse
+a macro to bridge the two codebases during the transition. Such is life,
+use your judgement and do the best possible under the circumstances.
+
 When printing or displaying the values of 64-bit integral data types,
 don't use "%lld", "%llu", "%llx", or "%llo" - not all platforms
 support "%ll" for printing 64-bit integral data types.  Instead, for
@@ -221,7 +219,8 @@ argument.  You must do
     call_routine2(xxx, format, ap);
     va_end(ap);
 
-rather
+rather than
+
     va_start(ap, format);
     call_routine1(xxx, format, ap);
     call_routine2(xxx, format, ap);
@@ -248,6 +247,7 @@ will not work with all compilers - you have to do
     }
 
 with some statement, even if it's a null statement, after the label.
+Preferably don't do it at all.
 
 Don't use "bzero()", "bcopy()", or "bcmp()"; instead, use the ANSI C
 routines

docbook/wsdg_src/WSDG_chapter_env_intro.adoc

@@ -122,11 +122,11 @@ Wireshark mailing lists available.
 
 ==== Programming Languages Used
 
-Most of Wireshark is implemented in C99.
+Most of Wireshark is implemented in C.
 A notable exception is the code in _ui/qt_, which is written in {cpp}.
 
 The typical task for a new Wireshark developer is to extend an existing dissector, or write a new dissector for a specific network protocol.
-Most dissectors are written in C99, so a good knowledge of C will be sufficient for Wireshark development in almost any case.
+Most dissectors are written in C11, so a good knowledge of C will be sufficient for Wireshark development in almost any case.
 Dissectors can also be written in Lua, which might be more suitable for your specific needs.
 As noted above, if you’re going to modify Wireshark’s user interface you will need a knowledge of {cpp}.