Error when compiling against librdkafka with g++ (as opposed to gcc), even with extern "C"

[winbatch]

Hi,

I had to make a change to get a C++ program to compile against librdkafka even with extern "C" of the header file. I think the error is less about C vs. C++ though but perhaps related to more strict error checking.

rd_kafka_message_errstr returns a const char *, however, it is returning the rkmessage->payload, which is a void *. I had to add cast it to const char * in the return statement to get it to compile.

[zokusai]

Hi,

I had to do the same using the diff patch:

diff --git a/rdkafka.h b/rdkafka.h
index 15e7abd..327fa71 100644
--- a/rdkafka.h
+++ b/rdkafka.h
@@ -477,7 +477,7 @@ rd_kafka_message_errstr (const rd_kafka_message_t *rkmessage) {
                return NULL;

        if (rkmessage->payload)
-               return rkmessage->payload;
+               return (const char *) rkmessage->payload;

        return rd_kafka_err2str(rkmessage->err);
 }

Also (maybe a Cygwin issue), I had to modify the Makefiles to discard the -Werror flag in order to compile:

diff --git a/examples/Makefile b/examples/Makefile
index 4f96afa..a142ec9 100644
--- a/examples/Makefile
+++ b/examples/Makefile
@@ -1,7 +1,7 @@
 EXAMPLES ?= rdkafka_example rdkafka_performance
 CC ?= cc
 CXX ?= g++
-CFLAGS += -g -Wall -Werror -Wfloat-equal -Wpointer-arith -O2 -I../
+CFLAGS += -g -Wall -Wfloat-equal -Wpointer-arith -O2 -I../
 CXXFLAGS += $(CFLAGS)
 LDFLAGS +=  ../librdkafka.a
 LDFLAGS += -lpthread -lz

diff --git a/Makefile b/Makefile
index 8fce227..dd06293 100644
--- a/Makefile
+++ b/Makefile
@@ -13,7 +13,7 @@ HDRS= rdkafka.h
 OBJS=  $(SRCS:.c=.o)
 DEPS=  ${OBJS:%.o=%.d}

-CFLAGS+=-O2 -Wall -Werror -Wfloat-equal -Wpointer-arith -fPIC -I.
+CFLAGS+=-O2 -Wall -Wfloat-equal -Wpointer-arith -fPIC -I.
 CFLAGS+=-g

 # Clang warnings to ignore

You may ask why Cygwin? Well, limitations of developer workstation on a restricted environment, not intended for the final deployment.

[edenhill]

Thank you both for reporting this.

[winbatch]

I think you might also want to do extern "C" around rdkafka.h. This way users who include it don't have to do it themselves when doing the include?

[edenhill]

I will release a proper C++ interface end of january.

[winbatch]

Looking forward to it. Will that be in partnership with https://github.com/adobe-research/libkafka or in competition? (I actually started using libkafka in the beginning and switched to librdkafka based on its better handling of my requirements)

[edenhill]

This will be a proper C++ interface on top of the librdkafka's C interface.