Extension written in C++ and undefined symbols

21 years ago by Peter 'iridium' Waller — view source — reply

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I've currently got some libraries written in C++ with various class
interfaces, I was going to write an interface between them and PHP but
got very stuck trying to get the extension to recognize any C++ linked
to it at all..

I spent quite a while searching the archives and google before posting
this, and found some advice telling me to set EXTRA_LDFLAGS = -lstdc++.
This seemed to fix the odd one or two things, I don't remember what now
because that was a while ago..

in my config.m4:

PHP_NEW_EXTENSION(nalicity, nalicity.c test.cpp, $ext_shared)

in test.cpp:

void blah()
{
printf( "\n\nBlah\n\n" );
}

in nalicity.c

PHP_FUNCTION(testfunction)
{
blah();
}

Doesn't work unless I rename test.cpp to test.c and change the
PHP_NEW_EXTENSION line accordingly. It compiles fine, I just get the error:

/usr/bin/php: relocation error:
/usr/lib/php/extensions/no-debug-non-zts-20020429/../../../../src/php/exts/nalicity/modules/nalicity.so:
undefined symbol: blah

when I try to run the PHP and load the dl(). As I said above though,
works fine as a plain old C file. Any ideas? I've stayed up all night
trying to figure it out but have gotten nowhere.

(and on an unrelated note, is there any way I can specify an absolute
path to dl()? I feel kinda stupid with all those ../..'s in there.)

Thanks in advance for any help,

Peter.

21 years ago by Vladimir Zidar — view source — reply

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When you need to access function compiled from C++ source code, you
need to declare it as extern "C", in order to tell the compiler to
generate function name that is compatible with C. Otherwise, compiler
will generate different name (will mangle it), and C won't be able to
find it.

So, write

extern "C" blah()
{
...
}

in test.cpp

I've currently got some libraries written in C++ with various class
interfaces, I was going to write an interface between them and PHP but
got very stuck trying to get the extension to recognize any C++ linked
to it at all..

I spent quite a while searching the archives and google before posting
this, and found some advice telling me to set EXTRA_LDFLAGS = -lstdc++.
This seemed to fix the odd one or two things, I don't remember what now
because that was a while ago..

in my config.m4:

PHP_NEW_EXTENSION(nalicity, nalicity.c test.cpp, $ext_shared)

in test.cpp:

void blah()
{
printf( "\n\nBlah\n\n" );
}

in nalicity.c

PHP_FUNCTION(testfunction)
{
blah();
}

Doesn't work unless I rename test.cpp to test.c and change the
PHP_NEW_EXTENSION line accordingly. It compiles fine, I just get the error:

/usr/bin/php: relocation error:
/usr/lib/php/extensions/no-debug-non-zts-20020429/../../../../src/php/exts/nalicity/modules/nalicity.so:
undefined symbol: blah

when I try to run the PHP and load the dl(). As I said above though,
works fine as a plain old C file. Any ideas? I've stayed up all night
trying to figure it out but have gotten nowhere.

(and on an unrelated note, is there any way I can specify an absolute
path to dl()? I feel kinda stupid with all those ../..'s in there.)

Thanks in advance for any help,

Peter.
--
Vladimir Zidar, Programmer

MindNever Foodstuff TRDG.
Head Office Branch

Tel: +381-63-550161, +385-98-9574261
http://www.mindnever.org, icq: 15414204, mail: mr_W@mindnever.org

21 years ago by Peter Waller — view source — reply

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Thank you muchly. It took considerable trial and error but I got it
working.

For any poor person that ends up searching this list and comes up to
this thread, in the config.m4 file add the lines

PHP_REQUIRE_CXX
EXTRA_LDFLAGS=-lstdc++

Somewhere.

Also make sure that your file ends in the extension .cpp.

Peter.

Vladimir Zidar wrote:

When you need to access function compiled from C++ source code, you
need to declare it as extern "C", in order to tell the compiler to
generate function name that is compatible with C. Otherwise, compiler
will generate different name (will mangle it), and C won't be able to
find it.

So, write

extern "C" blah()
{
...
}

in test.cpp

I've currently got some libraries written in C++ with various class
interfaces, I was going to write an interface between them and PHP but
got very stuck trying to get the extension to recognize any C++ linked
to it at all..

I spent quite a while searching the archives and google before posting
this, and found some advice telling me to set EXTRA_LDFLAGS = -lstdc++.
This seemed to fix the odd one or two things, I don't remember what now
because that was a while ago..

in my config.m4:

PHP_NEW_EXTENSION(nalicity, nalicity.c test.cpp, $ext_shared)

in test.cpp:

void blah()
{
printf( "\n\nBlah\n\n" );
}

in nalicity.c

PHP_FUNCTION(testfunction)
{
blah();
}

Doesn't work unless I rename test.cpp to test.c and change the
PHP_NEW_EXTENSION line accordingly. It compiles fine, I just get the error:

/usr/bin/php: relocation error:
/usr/lib/php/extensions/no-debug-non-zts-20020429/../../../../src/php/exts/nalicity/modules/nalicity.so:
undefined symbol: blah

when I try to run the PHP and load the dl(). As I said above though,
works fine as a plain old C file. Any ideas? I've stayed up all night
trying to figure it out but have gotten nowhere.

(and on an unrelated note, is there any way I can specify an absolute
path to dl()? I feel kinda stupid with all those ../..'s in there.)

Thanks in advance for any help,

Peter.

21 years ago by Asgeir Frimannsson — view source — reply

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Peter 'Iridium' Waller wrote:

I've currently got some libraries written in C++ with various class
interfaces, I was going to write an interface between them and PHP but
got very stuck trying to get the extension to recognize any C++ linked
to it at all..

Not an answer to your question (since it's allready answered), but might be
useful for some:

I was searching google the other day, and found a great starter-tutorial by
Jay Smith on how to write c++ extensions in ZE2.

http://bugs.tutorbuddy.com/php5cpp/php5cpp/index.html

regards
asgeir frimannsson