I am facing multiple issues with building my c++ code on Ubuntu 12.04. This code was building and running fine on RH Enterprise. I am using g++ 4.6.3. Here's the output of g++ -v. g++ -v Using built-in specs. COLLECT_GCC=g++ COLLECT_LTO_WRAPPER=/usr/lib/gcc/i686-linux-gnu/4.6/lto-wrapper Target: i686-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.6.3-1ubuntu5' --with-bugurl=file:///usr/share/doc/gcc-4.6/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.6 --enable-shared --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.6 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --enable-plugin --enable-objc-gc --enable-targets=all --disable-werror --with-arch-32=i686 --with-tune=generic --enable-checking=release --build=i686-linux-gnu --host=i686-linux-gnu --target=i686-linux-gnu Thread model: posix gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5) Here's a sample of my code: #include "Word.h" #include < string> using namespace std; pthread_mutex_t Word::_lock = PTHREAD_MUTEX_INITIALIZER; Word::Word(): _occurrences(1) { memset(_buf, 0, 25); } Word::Word(char *str): _occurrences(1) { memset(_buf, 0, 25); if (str != NULL) { strncpy(_buf, str, strlen(str)); } } g++ -c -ansi or g++ -c -std=c++98 or g++ -c -std=c++03, none of these options are able to build the code correctly. I get the following compilation errors: mriganka@ubuntu:~/WordCount$ make g++ -c -g -ansi Word.cpp -o Word.o Word.cpp: In constructor ‘Word::Word()’: Word.cpp:10:21: error: ‘memset’ was not declared in this scope Word.cpp: In constructor ‘Word::Word(char*)’: Word.cpp:16:21: error: ‘memset’ was not declared in this scope Word.cpp:19:34: error: ‘strlen’ was not declared in this scope Word.cpp:19:35: error: ‘strncpy’ was not declared in this scope Word.cpp: In member function ‘void Word::operator=(const Word&)’: Word.cpp:37:42: error: ‘strlen’ was not declared in this scope Word.cpp:37:43: error: ‘strncpy’ was not declared in this scope Word.cpp: In copy constructor ‘Word::Word(const Word&)’: Word.cpp:44:21: error: ‘memset’ was not declared in this scope Word.cpp:45:52: error: ‘strlen’ was not declared in this scope Word.cpp:45:53: error: ‘strncpy’ was not declared in this scope So basically g++ 4.6.3 on Ubuntu 12.04 is not able to recognize the standard c++ headers. And I am not finding a way out of this situation. Second problem: In order to make progress, I included < string.h instead of < string. But now I am facing linking errors with my message queue and pthread library functions. Here's the error that I am getting: mriganka@ubuntu:~/WordCount$ make g++ -c -g -ansi Word.cpp -o Word.o g++ -lrt -I/usr/lib/i386-linux-gnu Word.o HashMap.o main.o -o word_count main.o: In function `main': /home/mriganka/WordCount/main.cpp:75: undefined reference to `pthread_create' /home/mriganka/WordCount/main.cpp:90: undefined reference to `mq_open' /home/mriganka/WordCount/main.cpp:93: undefined reference to `mq_getattr' /home/mriganka/WordCount/main.cpp:113: undefined reference to `mq_send' /home/mriganka/WordCount/main.cpp:123: undefined reference to `pthread_join' /home/mriganka/WordCount/main.cpp:129: undefined reference to `mq_close' /home/mriganka/WordCount/main.cpp:130: undefined reference to `mq_unlink' main.o: In function `count_words(void*)': /home/mriganka/WordCount/main.cpp:151: undefined reference to `mq_open' /home/mriganka/WordCount/main.cpp:154: undefined reference to `mq_getattr' /home/mriganka/WordCount/main.cpp:162: undefined reference to `mq_timedreceive' collect2: ld returned 1 exit status Here's my makefile: CC=g++ CFLAGS=-c -g -ansi LDFLAGS=-lrt INC=-I/usr/lib/i386-linux-gnu SOURCES=Word.cpp HashMap.cpp main.cpp OBJECTS=$(SOURCES:.cpp=.o) EXECUTABLE=word_count all: $(SOURCES) $(EXECUTABLE) $(EXECUTABLE): $(OBJECTS) $(CC) $(LDFLAGS) $(INC) -pthread $(OBJECTS) -o $@ .cpp.o: $(CC) $(CFLAGS) $< -o $@ clean: rm -f *.o word_count Please help me to resolve both the issues. I searched online relentlessly for any solution of these problems, but no one seems to have encountered these issues.