Hello,
I didn't express myself when changes were made to the interface of property
classes,
resulting in the change of string to const char * but now, I experiment many
segfault
that are a direct result of these changes.
While I totally agree with the fact that input parameters should be const
char * to
avoid unnecessary memory allocations, I thing that making the same changes
to return
values such as in getStringValue is a big mistake. Here is why :
First, I am trying to build latest CVS flightgear with MSVC6 on Win2k. I am
surprised
that these problems do not show up with gcc (linux or Win2k)
First example :
/sim/logging/classes is tied and its getter function is :
/**
* Get the logging classes.
*/
static const char *
getLoggingClasses ()
{
sgDebugClass classes = logbuf::get_log_classes();
string result = "";
for (int i = 0; log_class_mappings[i].c != SG_UNDEFD; i++) {
if ((classes&log_class_mappings[i].c) > 0) {
if (!result.empty())
result += '|';
result += log_class_mappings[i].name;
}
}
return result.c_str();
}
the string result is a local variable and is not valid when getStringValue
returns.
Same problem with /sim/time/gmt-string and its getter function (from
fg_props.cxx) :
/**
* Return the GMT as a string.
*/
static const char *
getGMTString ()
{
string out;
char buf[16];
struct tm *t = globals->get_time_params()->getGmt();
sprintf(buf, " %.2d:%.2d:%.2d",
t->tm_hour, t->tm_min, t->tm_sec);
// cout << t << " " << buf << endl;
out = buf;
return out.c_str();
}
Here again the string out is destroyed before the return value has a chance
to be copied !
There are tons of similar examples. A quick and dirty fix would be to
transform those
locals static but with the loss of reentrancy (bye-bye threaded flightgear
!)
The changes also introduced the need for the caller to allocate a string or
to call strcmp
that I consider ugly (it's a matter of taste) in C++ programs and that obfus
cate the code.
The only way to avoid these memory management problems is to return a class
that can hold
and free its memory. The standard string class can do that, or we can create
a new string
class that do copy on write with reference counters.
I don't want to advocate for a compiler or an other but I am still perplex
about the fact
that no one noticed these problems with gcc !
Cheers,
-Fred
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