编译C ++代码时出错？

Question

This is my test.cpp :

#include <iostream.h>
class C {
public:
C();
~C();
};

int main()
{
C obj;
return 0;
}

When I compile it using the command g++ test.cpp , I get this error message:

In file included from /usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/backward/iostream.h:31,
                     from test.cpp:1:
    /usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/backward/backward_warning.h:32:2: warning: #warning This file includes at least one deprecated or antiquated header. Please consider using one of the 32 headers found in section 17.4.1.2 of the C++ standard. Examples include substituting the  header for the  header for C++ includes, or  instead of the deprecated header . To disable this warning use -Wno-deprecated.
    /cygdrive/c/Users/aswinik_sattaluri/AppData/Local/Temp/ccoYkiAS.o:test.cpp:(.text+0x131): undefined reference to `C::C()'
    /cygdrive/c/Users/aswinik_sattaluri/AppData/Local/Temp/ccoYkiAS.o:test.cpp:(.text+0x13c): undefined reference to `C::~C()'
    collect2: ld returned 1 exit status

Compiling with gcc test.cpp gives similar messages and even more:

In file included from /usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/backward/iostream.h:31,
                     from test.cpp:1:
    /usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/backward/backward_warning.h:32:2: warning: #warning This file includes at least one deprecated or antiquated header. Please consider using one of the 32 headers found in section 17.4.1.2 of the C++ standard. Examples include substituting the  header for the  header for C++ includes, or  instead of the deprecated header . To disable this warning use -Wno-deprecated.
    /cygdrive/c/Users/aswinik_sattaluri/AppData/Local/Temp/cc3ntGx0.o:test.cpp:(.text+0xd): undefined reference to `std::basic_string, std::allocator >::size() const'
    /cygdrive/c/Users/aswinik_sattaluri/AppData/Local/Temp/cc3ntGx0.o:test.cpp:(.text+0x60): undefined reference to `std::basic_string, std::allocator >::operator[](unsigned int) const'
    /cygdrive/c/Users/aswinik_sattaluri/AppData/Local/Temp/cc3ntGx0.o:test.cpp:(.text+0x9f): undefined reference to `std::basic_string, std::allocator >::operator[](unsigned int) const'
    /cygdrive/c/Users/aswinik_sattaluri/AppData/Local/Temp/cc3ntGx0.o:test.cpp:(.text+0xce): undefined reference to `std::basic_string, std::allocator >::operator[](unsigned int) const'
    /cygdrive/c/Users/aswinik_sattaluri/AppData/Local/Temp/cc3ntGx0.o:test.cpp:(.text+0x131): undefined reference to `C::C()'
    /cygdrive/c/Users/aswinik_sattaluri/AppData/Local/Temp/cc3ntGx0.o:test.cpp:(.text+0x13c): undefined reference to `C::~C()'
    /cygdrive/c/Users/aswinik_sattaluri/AppData/Local/Temp/cc3ntGx0.o:test.cpp:(.text+0x165): undefined reference to `std::ios_base::Init::Init()'
    /cygdrive/c/Users/aswinik_sattaluri/AppData/Local/Temp/cc3ntGx0.o:test.cpp:(.text+0x180): undefined reference to `std::ios_base::Init::~Init()'
    collect2: ld returned 1 exit status

Note that I haven't set LD_LIBRARY_PATH :

bash-3.2$ echo $LD_LIBRARY_PATH

    bash-3.2$

Answer 1

You have declared the existence of the C constructor and destructor, but have not provided implementations. Try:

class C {
public:
    C() {}
    ~C() {}
};

And, for C++ programs, use g++ to compile (as in your first attempt).

Answer 2

Replace

#include <iostream.h>

by

#include <iostream>

and provide implementations, at least empty, of the constructor and destructor of class C.

Answer 3

As you don't provide an actual question, I'd have to guess at what you'd like to know. Anyway, my 2c are:

• Don't use iostream.h , that header is pre-standard and well out of date. Use <iostream> instead
• You don't provide any implementation for the constructor and destructor of C , which is what the linker is complaining about.

Answer 4

You need to define your C constructor and destuctor:

C::C()
{
}

C::~C()
{
}

Also, stick with compiling with g++. If you look closely, the errors you get with compiling with gcc include everything you get with g++ plus extra errors.

Answer 5

You're including iostream.h instead of iostream , that's why you get a warning about this include. Also you have declared a constructor and a destructor for C but you haven't actually implemented it anywhere. Therefore the linker complains about undefined symbols.

You need to add implementations for the methods of C , like:

C::C() {
  // ...
}

Answer 6

use #include <iostream> instead of #include <iostream.h>

you should read the error properly.

Answer 7

One note about LD_LIBRARY_PATH - it doesn't concern you at compile or link time (then the linker will look in paths given with -L and some standard paths, like /usr/lib).

It's important When you run your application - the system will search for the shared libraries first in the paths, given in LD_LIBRARY_PATH.

http://www.linux.org/docs/ldp/howto/Program-Library-HOWTO/shared-libraries.html