Codeblocks succeeded in compiling, but gcc failes, Why? - c++

Question

I'm using ubuntu 18.
I'v installed codeblocks ide and bare gnu gcc compiler (command line) both
gcc version 7.4.0 (Ubuntu 7.4.0-1ubuntu1~18.04.1)
code blocks 16.01
I wrote a very simple code to create and print a string variable
Code blocks(with inbuilt gnu gcc compiler) succeeded in compiling. But bare gcc compiler failes
I've tried by including iostream and stdio also
#include <string>
using namespace std;
int main() {
string a = "I am learning C++";
printf("%s",a.c_str());
return 0;
}
codeblocks compiles it successfully and gives the output without raising an error. As well as sololearn online compiler also
I am learning C++
I got into the folder where the cpp file is and gave following command
gcc string_var.cpp -o string_var.out
Bt the bare gcc compiler gives some long stuff of compiler errors which i can't understand
/tmp/ccen8bfp.o: In function `main':
string_var.cpp:(.text+0x20): undefined reference to `std::allocator<char>::allocator()'
string_var.cpp:(.text+0x37): undefined reference to `std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(char const*, std::allocator<char> const&)'
string_var.cpp:(.text+0x43): undefined reference to `std::allocator<char>::~allocator()'
string_var.cpp:(.text+0x4f): undefined reference to `std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::c_str() const'
string_var.cpp:(.text+0x74): undefined reference to `std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::~basic_string()'
string_var.cpp:(.text+0x96): undefined reference to `std::allocator<char>::~allocator()'
string_var.cpp:(.text+0xb0): undefined reference to `std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::~basic_string()'
/tmp/ccen8bfp.o:(.data.rel.local.DW.ref.__gxx_personality_v0[DW.ref.__gxx_personality_v0]+0x0): undefined reference to `__gxx_personality_v0'
collect2: error: ld returned 1 exit status

Answer 1

The GNU Compiler Collection (GCC) can be used to compile many different languages. Some of those languages are common enough that they can use the same front-end program.
C and C++ are two such languages, and both can be compiled with the gcc front-end program. However, the gcc program by default is for C code, and because of that don't use some flags needed to build C++ programs. One such missing thing is that gcc doesn't link with the C++ standard library.
You can solve this by explicitly linking with the library:
gcc string_var.cpp -o string_var.out -lstdc++
Or, even simpler, use the front-end program for C++, g++:
g++ string_var.cpp -o string_var.out

Answer 2

gcc string_var.cpp -o string_var.out
gcc is a C compiler. You want to compile C++ code:
g++ string_var.cpp -o string_var.out
It just so happens that either gcc or g++ works insofar as compiling the actual code, the compiler understand that .cpp files contain C++ code, and proceeds accordingly.
However, when it times to linking the resulting object module, gcc does not provide the runtime C++ library to the linker (it still thinks it's just a C compiler, and has never heard of C++), resulting in your link failure.