FreeChainXenon/gcc
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Clean up examples for -Wdangling-pointer [PR109708]

Browse source 
gcc/ChangeLog
	PR c/109708
	* doc/invoke.texi (Warning Options): Fix broken example and
	clean up/reorganize the others.  Also describe what the short-form
	options mean.
This commit is contained in:
Sandra Loosemore 2024-01-21 02:36:19 +00:00
parent 11a5f26c4e
commit 29f931e39f
1 changed files with 42 additions and 30 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

72
gcc/doc/invoke.texi
View file

@ -9423,51 +9423,63 @@ levels but may yield different results with optimization than without.
@table @gcctabopt
@item -Wdangling-pointer=1
At level 1 the warning diagnoses only unconditional uses of dangling pointers.
For example
@smallexample
int f (int c1, int c2, x)
@{
char *p = strchr ((char[])@{ c1, c2 @}, c3);
// warning: dangling pointer to a compound literal
return p ? *p : 'x';
@}
@end smallexample
In the following function the store of the address of the local variable
@code{x} in the escaped pointer @code{*p} also triggers the warning.
@smallexample
void g (int **p)
@{
int x = 7;
// warning: storing the address of a local variable in *p
*p = &x;
@}
@end smallexample
At level 1, the warning diagnoses only unconditional uses of dangling pointers.
@item -Wdangling-pointer=2
At level 2, in addition to unconditional uses the warning also diagnoses
conditional uses of dangling pointers.
@end table
For example, because the array @var{a} in the following function is out of
scope when the pointer @var{s} that was set to point is used, the warning
triggers at this level.
The short form @option{-Wdangling-pointer} is equivalent to
@option{-Wdangling-pointer=2}, while @option{-Wno-dangling-pointer} and
@option{-Wdangling-pointer=0} have the same effect of disabling the warnings.
@option{-Wdangling-pointer=2} is included in @option{-Wall}.
This example triggers the warning at level 1; the address of the unnamed
temporary is unconditionally referenced outside of its scope.
@smallexample
void f (char *s)
char f (char c1, char c2, char c3)
@{
char *p;
@{
p = (char[]) @{ c1, c2, c3 @};
@}
// warning: using dangling pointer 'p' to an unnamed temporary
return *p;
@}
@end smallexample
In the following function the store of the address of the local variable
@code{x} in the escaped pointer @code{*p} triggers the warning at
level 1.
@smallexample
void g (int **p)
@{
int x = 7;
// warning: storing the address of local variable 'x' in '*p'
*p = &x;
@}
@end smallexample
In this example, the array @var{a} is out of
scope when the pointer @var{s} is used. Since the code that sets @code{s}
is conditional, the warning triggers at level 2.
@smallexample
extern void frob (const char *);
void h (char *s)
@{
if (!s)
@{
char a[12] = "tmpname";
s = a;
@}
// warning: dangling pointer to a may be used
strcat (s, ".tmp");
...
// warning: dangling pointer 's' to 'a' may be used
frob (s);
@}
@end smallexample
@end table
@option{-Wdangling-pointer=2} is included in @option{-Wall}.
@opindex Wdate-time
@opindex Wno-date-time