| Message ID | 21804bb93c4544208a445d1286efa8b6@gmail.com |
|---|---|
| State | New |
| Headers | show |
Michael Witten: > This commit adds 'const' qualifiers to the parameters. > > --- > libavformat/avio.h | 2 +- > libavformat/protocols.c | 2 +- > 2 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/libavformat/avio.h b/libavformat/avio.h > index 0b35409787..3b92cf742a 100644 > --- a/libavformat/avio.h > +++ b/libavformat/avio.h > @@ -786,7 +786,7 @@ int avio_close_dyn_buf(AVIOContext *s, uint8_t **pbuffer); > * > * @return A static string containing the name of current protocol or NULL > */ > -const char *avio_enum_protocols(void **opaque, int output); > +const char *avio_enum_protocols(void **const opaque, const int output); > > /** > * Get AVClass by names of available protocols. > diff --git a/libavformat/protocols.c b/libavformat/protocols.c > index e0b3405ab8..e671c5ab6a 100644 > --- a/libavformat/protocols.c > +++ b/libavformat/protocols.c > @@ -91,7 +91,7 @@ const AVClass *ff_urlcontext_child_class_iterate(void **iter) > return ret; > } > > -const char *avio_enum_protocols(void **opaque, int output) > +const char *avio_enum_protocols(void **const opaque, const int output) > { > const URLProtocol *const *p = *opaque; > > This thing makes nothing more const-correct at all; C uses call be value, so we only deal with our own copy of opaque which we may modify as we please. The reason for the const-incorrectness lies in the fact that this function makes *opaque point to something const (namely an entry in a const list of pointers (each pointing to a const protocol, but that is irrelevant)), so that the user now has a pointer whose pointed to-type is not const-qualified, despite the actual target being const. See here: https://patchwork.ffmpeg.org/project/ffmpeg/patch/20190821090438.10260-2-andreas.rheinhardt@gmail.com/ for how to fix the const-correctness if one wants to keep the general design of the functions. See libavformat/allformats.c, libavcodec/allcodecs.c, libavfilter/allfilters.c for the other approach (that involves storing an index in the pointer). - Andreas
| Michael Witten: | | > -const char *avio_enum_protocols(void **opaque, int output) | > +const char *avio_enum_protocols(void **const opaque, const int output) | | Andreas Rheinhardt: | | > This thing makes nothing more const-correct at all; C uses call be | > value, so we only deal with our own copy of opaque which we may modify | > as we please. | > The reason for the const-incorrectness lies in the fact that this | > function makes *opaque point to something const (namely an entry in a | > const list of pointers (each pointing to a const protocol, but that is | > irrelevant)), so that the user now has a pointer whose pointed to-type | > is not const-qualified, despite the actual target being const. | > See here: | > https://patchwork.ffmpeg.org/project/ffmpeg/patch/20190821090438.10260-2-andreas.rheinhardt@gmail.com/ | > for how to fix the const-correctness if one wants to keep the general | > design of the functions. See libavformat/allformats.c, | > libavcodec/allcodecs.c, libavfilter/allfilters.c for the other approach | > (that involves storing an index in the pointer). | > | > - Andreas * The general design of the functions has not been altered by this series. * The previous patch fixed the const incorrectness as warned by the compiler. This patch merely improves the const correctness in general. * We don't want to modify those parameters as we please, and so we'd like to ask the compiler to remind us of that fact as necessary. It's const-correct in the sense that it expresses the following fact: Those variables are not going to be changed; if there is no intention to modify a variable, then it's good practice to mark that variable as const. Because this function is being edited, it's a good time to sprinkle the 'const' keyword around, as a matter of mental hygiene. Sincerely, Michael Witten
diff --git a/libavformat/avio.h b/libavformat/avio.h index 0b35409787..3b92cf742a 100644 --- a/libavformat/avio.h +++ b/libavformat/avio.h @@ -786,7 +786,7 @@ int avio_close_dyn_buf(AVIOContext *s, uint8_t **pbuffer); * * @return A static string containing the name of current protocol or NULL */ -const char *avio_enum_protocols(void **opaque, int output); +const char *avio_enum_protocols(void **const opaque, const int output); /** * Get AVClass by names of available protocols. diff --git a/libavformat/protocols.c b/libavformat/protocols.c index e0b3405ab8..e671c5ab6a 100644 --- a/libavformat/protocols.c +++ b/libavformat/protocols.c @@ -91,7 +91,7 @@ const AVClass *ff_urlcontext_child_class_iterate(void **iter) return ret; } -const char *avio_enum_protocols(void **opaque, int output) +const char *avio_enum_protocols(void **const opaque, const int output) { const URLProtocol *const *p = *opaque;