C++ / JNI memory leakage, help needed

[Sambucus]

Hi group!

I am using C++ and java with JNI to get some text in a RICHEDIT to my
java program. I do so by accessing a C++ method every second. It all
works fine except that it leaks memory every call I make to the C++
method.

Can anyone please help me with this problem? I am not sure wether the
leakage is in the C++ or java code. But i guess it's on the C++ side
since I'm kind of newbee there.

Is there perhaps a way to release the memory allocated for a LPTSTR in
C++?
Please take a look at the code below, it is the method i call every
second from java. I belive it is the LPTSTR that is leaking, since it
leaks more when the string gets larger.

<---------------
LPTSTR output;

JNIEXPORT jstring JNICALL
Java_JNIHandler _getDealerOutpu t(JNIEnv *env, jobject obj){

size = SendMessage(
(HWND) textarea, // handle to destination window
WM_GETTEXTLENGT H, // message to send
(WPARAM) 0,
(LPARAM) 0 ) +1;

output = new TCHAR[size];

SendMessage(tex tarea,
WM_GETTEXT,
size,
(LPARAM)(void*) output);

return env->NewStringUTF(d ealerStr);

}
------------------>

I have tried to release the memory allocated when the NewStringUTF is
made with the JNI.h method env -> ReleaseStringUT FChars(str,
dealerStr) to no avail.
I hae also tried to use a try/finally block and in the finally set:
output= NULL; delete output; but there is no difference.

Cheers
Andreas

[Jeff Schwab]

John Harrison wrote:

"Sambucus" <an************ ***@aetdata.com > wrote in message
news:d3******** *************** ***@posting.goo gle.com...

Hi group!

I am using C++ and java with JNI to get some text in a RICHEDIT to my
java program. I do so by accessing a C++ method every second. It all
works fine except that it leaks memory every call I make to the C++
method.

Can anyone please help me with this problem? I am not sure wether the
leakage is in the C++ or java code. But i guess it's on the C++ side
since I'm kind of newbee there.

Is there perhaps a way to release the memory allocated for a LPTSTR in
C++?
Please take a look at the code below, it is the method i call every
second from java. I belive it is the LPTSTR that is leaking, since it
leaks more when the string gets larger.

<---------------
LPTSTR output;

JNIEXPORT jstring JNICALL
Java_JNIHandl er_getDealerOut put(JNIEnv *env, jobject obj){

size = SendMessage(
(HWND) textarea, // handle to destination window
WM_GETTEXTLEN GTH, // message to send
(WPARAM) 0,
(LPARAM) 0 ) +1;

output = new TCHAR[size];

SendMessage(t extarea,
WM_GETTEXT,
size,
(LPARAM)(void *)output);

return env->NewStringUTF(d ealerStr);

}
------------------>

I have tried to release the memory allocated when the NewStringUTF is
made with the JNI.h method env -> ReleaseStringUT FChars(str,
dealerStr) to no avail.
I hae also tried to use a try/finally block and in the finally set:
output= NULL; delete output; but there is no difference.

finally is not part of the C++ language

Try this

jstring res = env->NewStringUTF(d ealerStr);
delete[] output;
return res;

I guess you are more of a Java programmer than a C++ programmer.

Another method would be to use a vector, then you wouldn't have to worry
about memory allocation.

size = SendMessage(tex tarea, WM_GETTEXTLENGT H, 0, 0);
std::vector<TCH AR> output(size + 1);
SendMessage(tex tarea, WM_GETTEXT, size, (LPARAM)(void*) &output[0]);
return env->NewStringUTF(& output[0]);

I'm a bit hazy on the Windows and JNI details but the bottom line is that if
you allocate memory with new[] then you have to free it with delete[], and
if you use a vector then you don't have to deallocate at all.

What John said, but consider using a std::basic_stri ng<TCHAR> instead of
std::vector<TCH AR>. The basic string in C++ has more Java-like syntax,
e.g. the operator [ ] is range-checked, and concatenation can be done
with operator +.

[Chris Uppal]

Sambucus wrote:

output = new TCHAR[size];
This store is allocated but never freed. You need code to free it somewhere,
like:

delete [] output;
output = 0; // or = NULL if you prefer

return env->NewStringUTF(d ealerStr);

Where does dealerStr come from ? Is this supposed to be 'output' ? I so then
you should probably make 'output' be a local variable of
Java_JNIHandler _getDealerOutpu t().

I think you also may have problems with passing the text from the window to
NewStringUTF(), that function requires bytes in a specific format that isn't
"just plain text" (though it'll work with plain text in many cases). I don't
think that'd be causing memory leaks, though, just "strange" Strings returned
from your native method (or possibly crashing the JVM ;-)

-- chris

[John Harrison]

>

What John said, but consider using a std::basic_stri ng<TCHAR> instead of
std::vector<TCH AR>. The basic string in C++ has more Java-like syntax,
e.g. the operator [ ] is range-checked, and concatenation can be done
with operator +.

But the problem with std::basic_stri ng is that you cannot get a writable
pointer from it. Therefore it's not suitable for passing to SendMessage(win ,
WM_GETTEXT ...).

john

[John Harrison]

"Sambucus" <an************ ***@aetdata.com > wrote in message
news:d3******** *************** ***@posting.goo gle.com...

Hi group!

I am using C++ and java with JNI to get some text in a RICHEDIT to my
java program. I do so by accessing a C++ method every second. It all
works fine except that it leaks memory every call I make to the C++
method.

Can anyone please help me with this problem? I am not sure wether the
leakage is in the C++ or java code. But i guess it's on the C++ side
since I'm kind of newbee there.

Is there perhaps a way to release the memory allocated for a LPTSTR in
C++?
Please take a look at the code below, it is the method i call every
second from java. I belive it is the LPTSTR that is leaking, since it
leaks more when the string gets larger.

<---------------
LPTSTR output;

JNIEXPORT jstring JNICALL
Java_JNIHandler _getDealerOutpu t(JNIEnv *env, jobject obj){

size = SendMessage(
(HWND) textarea, // handle to destination window
WM_GETTEXTLENGT H, // message to send
(WPARAM) 0,
(LPARAM) 0 ) +1;

output = new TCHAR[size];

SendMessage(tex tarea,
WM_GETTEXT,
size,
(LPARAM)(void*) output);

return env->NewStringUTF(d ealerStr);

}
------------------>

I have tried to release the memory allocated when the NewStringUTF is
made with the JNI.h method env -> ReleaseStringUT FChars(str,
dealerStr) to no avail.
I hae also tried to use a try/finally block and in the finally set:
output= NULL; delete output; but there is no difference.

finally is not part of the C++ language

Try this

jstring res = env->NewStringUTF(d ealerStr);
delete[] output;
return res;

I guess you are more of a Java programmer than a C++ programmer.

Another method would be to use a vector, then you wouldn't have to worry
about memory allocation.

size = SendMessage(tex tarea, WM_GETTEXTLENGT H, 0, 0);
std::vector<TCH AR> output(size + 1);
SendMessage(tex tarea, WM_GETTEXT, size, (LPARAM)(void*) &output[0]);
return env->NewStringUTF(& output[0]);

I'm a bit hazy on the Windows and JNI details but the bottom line is that if
you allocate memory with new[] then you have to free it with delete[], and
if you use a vector then you don't have to deallocate at all.

john

[Jeff Schwab]

John Harrison wrote:

What John said, but consider using a std::basic_stri ng<TCHAR> instead of
std::vector<T CHAR>. The basic string in C++ has more Java-like syntax,
e.g. the operator [ ] is range-checked, and concatenation can be done
with operator +.

But the problem with std::basic_stri ng is that you cannot get a writable
pointer from it. Therefore it's not suitable for passing to SendMessage(win ,
WM_GETTEXT ...).

Thanks for clarifying, John. I don't know about SendMessage, and there
was no prototype in the OP. I see now that the string was given no
initializer, so it will need to be written.

Why use a vector, though, instead of an automatic array?

[Jeff Schwab]

John Harrison wrote:

"Sambucus" <an************ ***@aetdata.com > wrote in message
news:d3******** *************** ***@posting.goo gle.com...

Hi group!

I am using C++ and java with JNI to get some text in a RICHEDIT to my
java program. I do so by accessing a C++ method every second. It all
works fine except that it leaks memory every call I make to the C++
method.

Can anyone please help me with this problem? I am not sure wether the
leakage is in the C++ or java code. But i guess it's on the C++ side
since I'm kind of newbee there.

Is there perhaps a way to release the memory allocated for a LPTSTR in
C++?
Please take a look at the code below, it is the method i call every
second from java. I belive it is the LPTSTR that is leaking, since it
leaks more when the string gets larger.

<---------------
LPTSTR output;

JNIEXPORT jstring JNICALL
Java_JNIHandl er_getDealerOut put(JNIEnv *env, jobject obj){

size = SendMessage(
(HWND) textarea, // handle to destination window
WM_GETTEXTLEN GTH, // message to send
(WPARAM) 0,
(LPARAM) 0 ) +1;

output = new TCHAR[size];

SendMessage(t extarea,
WM_GETTEXT,
size,
(LPARAM)(void *)output);

return env->NewStringUTF(d ealerStr);

}
------------------>

I have tried to release the memory allocated when the NewStringUTF is
made with the JNI.h method env -> ReleaseStringUT FChars(str,
dealerStr) to no avail.
I hae also tried to use a try/finally block and in the finally set:
output= NULL; delete output; but there is no difference.

finally is not part of the C++ language

Try this

jstring res = env->NewStringUTF(d ealerStr);
delete[] output;
return res;

I guess you are more of a Java programmer than a C++ programmer.

Another method would be to use a vector, then you wouldn't have to worry
about memory allocation.

size = SendMessage(tex tarea, WM_GETTEXTLENGT H, 0, 0);
std::vector<TCH AR> output(size + 1);
SendMessage(tex tarea, WM_GETTEXT, size, (LPARAM)(void*) &output[0]);
return env->NewStringUTF(& output[0]);

I'm a bit hazy on the Windows and JNI details but the bottom line is that if
you allocate memory with new[] then you have to free it with delete[], and
if you use a vector then you don't have to deallocate at all.

What John said, but consider using a std::basic_stri ng<TCHAR> instead of
std::vector<TCH AR>. The basic string in C++ has more Java-like syntax,
e.g. the operator [ ] is range-checked, and concatenation can be done
with operator +.

[John Harrison]

"Jeff Schwab" <je******@comca st.net> wrote in message
news:Q4******** ************@co mcast.com...

John Harrison wrote:

What John said, but consider using a std::basic_stri ng<TCHAR> instead of
std::vector<T CHAR>. The basic string in C++ has more Java-like syntax,
e.g. the operator [ ] is range-checked, and concatenation can be done
with operator +.

But the problem with std::basic_stri ng is that you cannot get a writable
pointer from it. Therefore it's not suitable for passing to SendMessage(win , WM_GETTEXT ...).

Thanks for clarifying, John. I don't know about SendMessage, and there
was no prototype in the OP. I see now that the string was given no
initializer, so it will need to be written.

Why use a vector, though, instead of an automatic array?

Because the size isn't known at compile time. Some compilers support arrays
whose size is not known until runtime but its not standard C++.

This is all Windows detail but

SendMessage(tex tarea, WM_GETTEXTLENGT H, ...

gets the length of text and

SendMessage(tex tarea, WM_GETTEXT, ...

gets the actual characters.

john

[John Harrison]

>

What John said, but consider using a std::basic_stri ng<TCHAR> instead of
std::vector<TCH AR>. The basic string in C++ has more Java-like syntax,
e.g. the operator [ ] is range-checked, and concatenation can be done
with operator +.

But the problem with std::basic_stri ng is that you cannot get a writable
pointer from it. Therefore it's not suitable for passing to SendMessage(win ,
WM_GETTEXT ...).

john

[Jeff Schwab]

John Harrison wrote:

What John said, but consider using a std::basic_stri ng<TCHAR> instead of
std::vector<T CHAR>. The basic string in C++ has more Java-like syntax,
e.g. the operator [ ] is range-checked, and concatenation can be done
with operator +.

But the problem with std::basic_stri ng is that you cannot get a writable
pointer from it. Therefore it's not suitable for passing to SendMessage(win ,
WM_GETTEXT ...).

Thanks for clarifying, John. I don't know about SendMessage, and there
was no prototype in the OP. I see now that the string was given no
initializer, so it will need to be written.

Why use a vector, though, instead of an automatic array?