Re: [wwwdocs] Document C++ null pointer constant changes in gcc-7/porting_to.html
On 09/04/17 19:58 -0600, Sandra Loosemore wrote:
On 04/07/2017 03:25 AM, Jonathan Wakely wrote:
This issue caused a lot of build failures during the GCC mass rebuilds
for Fedora, but isn't in the porting to guide yet.
Is this accurate and clear enough for casual readers?
Index: htdocs/gcc-7/porting_to.html
===
RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-7/porting_to.html,v
retrieving revision 1.13
diff -u -r1.13 porting_to.html
--- htdocs/gcc-7/porting_to.html6 Apr 2017 17:12:16 - 1.13
+++ htdocs/gcc-7/porting_to.html7 Apr 2017 09:25:06 -
@@ -118,6 +118,39 @@
with GCC 7 and some are compiled with older releases.
+Null pointer constants
+
+
+When compiling as C++11 or later, GCC 7 follows the revised definition of a
+null pointer constant. This means conversions to pointers from other
+types of constant (such as character literals and boolean literals) will now
+be rejected.
+
Nit pick: s/will now be rejected/are now rejected/
since "now" means we are describing GCC's current behavior, not future
behavior. :-)
If you write such code (or try to compile existing code like that) it
will now be rejected - that's the first conditional isn't it?
"It's started raining and if you go outside again you will now get
wet."
Anyway, I've committed the attached patch with that change and a
similar one you noted previously for GCC 5.
? htdocs/gcc-7/porting_to.TODO
Index: htdocs/gcc-5/porting_to.html
===
RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-5/porting_to.html,v
retrieving revision 1.11
diff -u -r1.11 porting_to.html
--- htdocs/gcc-5/porting_to.html 21 Jan 2016 22:20:29 - 1.11
+++ htdocs/gcc-5/porting_to.html 10 Apr 2017 11:48:09 -
@@ -398,7 +398,7 @@
GCC 5 implements
http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1579;>DR 1579
-which means that in a function like:
+which means that when compiling a function like:
X
@@ -409,17 +409,17 @@
}
-GCC will first attempt to construct the return value as if y
-were an rvalue, and if that fails then it will try again for an lvalue
+GCC first attempts to construct the return value as though y
+were an rvalue, and if that fails then it tries again using an lvalue
(all C++11 compilers already do this when returning a variable of the
-same type as the function returns, but now they are required to do it
+same type as the function returns, but now they are also required to do it
when the types are not the same).
-This will change the constructor that gets called in some cases,
+This changes the constructor that gets called in some cases,
for example it might now call X(Y) instead of
X(const Y).
-In most cases the only observable difference will be code that runs faster
+In most cases the only observable difference is code that runs faster
(by moving instead of copying) but if it causes a problem the new behavior
can be prevented by ensuring the compiler treats y as an lvalue,
using return X(y); or
Index: htdocs/gcc-7/porting_to.html
===
RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-7/porting_to.html,v
retrieving revision 1.13
diff -u -r1.13 porting_to.html
--- htdocs/gcc-7/porting_to.html 6 Apr 2017 17:12:16 - 1.13
+++ htdocs/gcc-7/porting_to.html 10 Apr 2017 11:48:09 -
@@ -118,6 +118,39 @@
with GCC 7 and some are compiled with older releases.
+Null pointer constants
+
+
+When compiling as C++11 or later, GCC 7 follows the revised definition of a
+null pointer constant. This means conversions to pointers from other
+types of constant (such as character literals and boolean literals) are now
+rejected.
+
+
+void* f() {
+ char* p = '\0';
+ return false;
+}
+
+
+
+error: invalid conversion from 'char' to 'char*' [-fpermissive]
+ char* p = '\0';
+ ^~~~
+error: cannot convert 'bool' to 'void*' in return
+ return false;
+ ^
+
+
+
+Such code should be fixed to use a valid null pointer constant such as
+0 or nullptr. Care should be taken when fixing
+invalid uses of '\0' as a pointer, as it may not be clear whether
+the intention was to create a null pointer (p = 0;), to create an
+empty string (p = "";), or to write a null terminator to the
+string (*p = '\0';).
+
+
Header dependency changes
Re: [wwwdocs] Document C++ null pointer constant changes in gcc-7/porting_to.html
On 04/07/2017 03:25 AM, Jonathan Wakely wrote: This issue caused a lot of build failures during the GCC mass rebuilds for Fedora, but isn't in the porting to guide yet. Is this accurate and clear enough for casual readers? Index: htdocs/gcc-7/porting_to.html === RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-7/porting_to.html,v retrieving revision 1.13 diff -u -r1.13 porting_to.html --- htdocs/gcc-7/porting_to.html6 Apr 2017 17:12:16 - 1.13 +++ htdocs/gcc-7/porting_to.html7 Apr 2017 09:25:06 - @@ -118,6 +118,39 @@ with GCC 7 and some are compiled with older releases. +Null pointer constants + + +When compiling as C++11 or later, GCC 7 follows the revised definition of a +null pointer constant. This means conversions to pointers from other +types of constant (such as character literals and boolean literals) will now +be rejected. + Nit pick: s/will now be rejected/are now rejected/ since "now" means we are describing GCC's current behavior, not future behavior. :-) -Sandra
Re: [wwwdocs] Document C++ null pointer constant changes in gcc-7/porting_to.html
On Fri, Apr 07, 2017 at 10:25:21AM +0100, Jonathan Wakely wrote:
> This issue caused a lot of build failures during the GCC mass rebuilds
> for Fedora, but isn't in the porting to guide yet.
>
> Is this accurate and clear enough for casual readers?
Looks fine to me.
> Index: htdocs/gcc-7/porting_to.html
> ===
> RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-7/porting_to.html,v
> retrieving revision 1.13
> diff -u -r1.13 porting_to.html
> --- htdocs/gcc-7/porting_to.html 6 Apr 2017 17:12:16 - 1.13
> +++ htdocs/gcc-7/porting_to.html 7 Apr 2017 09:25:06 -
> @@ -118,6 +118,39 @@
> with GCC 7 and some are compiled with older releases.
>
>
> +Null pointer constants
> +
> +
> +When compiling as C++11 or later, GCC 7 follows the revised definition of a
> +null pointer constant. This means conversions to pointers from other
> +types of constant (such as character literals and boolean literals) will now
> +be rejected.
> +
> +
> +void* f() {
> + char* p = '\0';
> + return false;
> +}
> +
> +
> +
> +error: invalid conversion from 'char' to
> 'char*' [-fpermissive]
> + char* p = '\0';
> + ^~~~
> +error: cannot convert 'bool' to
> 'void*' in return
> + return false;
> + ^
> +
> +
> +
> +Such code should be fixed to use a valid null pointer constant such as
> +0 or nullptr. Care should be taken when fixing
> +invalid uses of '\0' as a pointer, as it may not be clear
> whether
> +the intention was to create a null pointer (p = 0;), to create
> an
> +empty string (p = "";), or to write a null terminator to the
> +string (*p = '\0';).
> +
> +
> Header dependency changes
>
>
Marek
[wwwdocs] Document C++ null pointer constant changes in gcc-7/porting_to.html
This issue caused a lot of build failures during the GCC mass rebuilds
for Fedora, but isn't in the porting to guide yet.
Is this accurate and clear enough for casual readers?
Index: htdocs/gcc-7/porting_to.html
===
RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-7/porting_to.html,v
retrieving revision 1.13
diff -u -r1.13 porting_to.html
--- htdocs/gcc-7/porting_to.html 6 Apr 2017 17:12:16 - 1.13
+++ htdocs/gcc-7/porting_to.html 7 Apr 2017 09:25:06 -
@@ -118,6 +118,39 @@
with GCC 7 and some are compiled with older releases.
+Null pointer constants
+
+
+When compiling as C++11 or later, GCC 7 follows the revised definition of a
+null pointer constant. This means conversions to pointers from other
+types of constant (such as character literals and boolean literals) will now
+be rejected.
+
+
+void* f() {
+ char* p = '\0';
+ return false;
+}
+
+
+
+error: invalid conversion from 'char' to 'char*' [-fpermissive]
+ char* p = '\0';
+ ^~~~
+error: cannot convert 'bool' to 'void*' in return
+ return false;
+ ^
+
+
+
+Such code should be fixed to use a valid null pointer constant such as
+0 or nullptr. Care should be taken when fixing
+invalid uses of '\0' as a pointer, as it may not be clear whether
+the intention was to create a null pointer (p = 0;), to create an
+empty string (p = "";), or to write a null terminator to the
+string (*p = '\0';).
+
+
Header dependency changes
