string to float in gcc - c++

Question

#include <iostream>
#include <stdlib.h>
using namespace std;
int main()
{
string a;
cin>>a;
float v=strtof(a.c_str(),NULL);
cout<<v;
}
The above code works in g++ compiler. But in gcc its reporting following error.
/tmp/ccz60ueB.o: In function `main':
test1.cpp:(.text+0x12): undefined reference to `std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string()'
test1.cpp:(.text+0x21): undefined reference to `std::cin'
test1.cpp:(.text+0x26): undefined reference to `std::basic_istream<char, std::char_traits<char> >& std::operator>><char, std::char_traits<char>, std::allocator<char> >(std::basic_istream<char, std::char_traits<char> >&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)'
test1.cpp:(.text+0x32): undefined reference to `std::basic_string<char, std::char_traits<char>, std::allocator<char> >::c_str() const'
test1.cpp:(.text+0x55): undefined reference to `std::cout'
test1.cpp:(.text+0x5a): undefined reference to `std::basic_ostream<char, std::char_traits<char> >::operator<<(float)'
test1.cpp:(.text+0x66): undefined reference to `std::basic_string<char, std::char_traits<char>, std::allocator<char> >::~basic_string()'
test1.cpp:(.text+0x81): undefined reference to `std::basic_string<char, std::char_traits<char>, std::allocator<char> >::~basic_string()'
/tmp/ccz60ueB.o: In function `__static_initialization_and_destruction_0(int, int)':
test1.cpp:(.text+0xac): undefined reference to `std::ios_base::Init::Init()'
test1.cpp:(.text+0xb1): undefined reference to `std::ios_base::Init::~Init()'
/tmp/ccz60ueB.o:(.eh_frame+0x13): undefined reference to `__gxx_personality_v0'
collect2: ld returned 1 exit status

Answer 1

You have to use g++ (or any C++ compiler) so it links with the C++ version of the library std. You shouldn't try to compile C++ code with a C compiler.

Answer 2

The following example works just fine for g++.
std::string asd="12312332434";
float as;
istringstream a;
a.str(asd);
a>>as;
cout<<as;
The following example must work fine for gcc.
//#include <stdio.h>
//#include <stdlib.h>
char asd[10];
float i;
fgets ( asd, 10, stdin );
i = atoi (asd);

Answer 3

gcc detects the language based on the file extension, so it can compile C++. However, you need to tell it to link against libstdc++.
For example:
gcc -o test test.cc -lstdc++
However, I'm not sure why you would do this.