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core: C++-ify membuffer

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C-style memory management is a pain and nearly nobody seems to get
it right. Add a C++-version of membuffer that frees the buffer
when it gets out-of-scope. Originally, I was thinking about
conditionally adding a constructor/destructor pair when compiling
with C++. But then decided to create a derived class membufferpp,
because it would be extremely confusing to have behavioral change
when changing a source from from C to C++ or vice-versa.

Also add a comment about the dangers of returned pointer: They
become dangling on changes to the membuffer.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
This commit is contained in:
Berthold Stoeger 2021-07-20 07:24:07 +02:00 committed by Dirk Hohndel
parent 0c84f369c3
commit f142e9a9c6
5 changed files with 26 additions and 9 deletions
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2
Subsurface-mobile.pro
View file

@ -86,7 +86,7 @@ SOURCES += subsurface-mobile-main.cpp \
core/divesite.c \
core/equipment.c \
core/gas.c \
core/membuffer.c \
core/membuffer.cpp \
core/selection.cpp \
core/sha1.c \
core/string-format.cpp \

2
core/CMakeLists.txt
View file

@ -122,7 +122,7 @@ set(SUBSURFACE_CORE_LIB_SRCS
libdivecomputer.h
liquivision.c
load-git.c
membuffer.c
membuffer.cpp
membuffer.h
metadata.cpp
metadata.h

2
core/format.cpp
View file

@ -397,7 +397,6 @@ int vasprintf_loc(char **dst, const char *cformat, va_list ap)
return utf8.size();
}
// This function is defined here instead of membuffer.c, because it needs to access QString.
extern "C" void put_vformat_loc(struct membuffer *b, const char *fmt, va_list args)
{
QByteArray utf8 = vqasprintf_loc(fmt, args).toUtf8();
@ -408,4 +407,3 @@ extern "C" void put_vformat_loc(struct membuffer *b, const char *fmt, va_list ar
memcpy(b->buffer + b->len, data, utf8_size);
b->len += utf8_size;
}

12
core/membuffer.c → core/membuffer.cpp
View file

@ -12,6 +12,16 @@
#include "units.h"
#include "membuffer.h"
membufferpp::membufferpp()
: membuffer{0, 0, nullptr}
{
}
membufferpp::~membufferpp()
{
free_buffer(this);
}
/* Only for internal use */
static char *detach_buffer(struct membuffer *b)
{
@ -66,7 +76,7 @@ void make_room(struct membuffer *b, unsigned int size)
char *n;
/* round it up to not reallocate all the time.. */
needed = needed * 9 / 8 + 1024;
n = realloc(b->buffer, needed);
n = (char *)realloc(b->buffer, needed);
if (!n)
oom();
b->buffer = n;

17
core/membuffer.h
View file

@ -36,10 +36,6 @@
#ifndef MEMBUFFER_H
#define MEMBUFFER_H
#ifdef __cplusplus
extern "C" {
#endif
#include <ctype.h>
#include <stdio.h>
#include <stdarg.h>
@ -50,6 +46,17 @@ struct membuffer {
char *buffer;
};
#ifdef __cplusplus
// In C++ code use this - it automatically frees the buffer, when going out of scope.
struct membufferpp : public membuffer {
membufferpp();
~membufferpp();
};
extern "C" {
#endif
#ifdef __GNUC__
#define __printf(x, y) __attribute__((__format__(__printf__, x, y)))
#else
@ -64,6 +71,8 @@ extern void put_bytes(struct membuffer *, const char *, int);
extern void put_string(struct membuffer *, const char *);
extern void put_quoted(struct membuffer *, const char *, int, int);
extern void strip_mb(struct membuffer *);
/* The pointer obtained by mb_cstring is invalidated by any modifictation to the membuffer! */
extern const char *mb_cstring(struct membuffer *);
extern __printf(2, 0) void put_vformat(struct membuffer *, const char *, va_list);
extern __printf(2, 0) void put_vformat_loc(struct membuffer *, const char *, va_list);