Simple code will not compile with clang or gcc but it will with g++

Question

Why does my cpp code fail when I try to build it with gcc or clang but not g++? With gcc or clang I get undefined reference errors, but no errors with g++

This is my simple program:

#include <iostream>
using namespace std;
int main() {
      cout << "Hello World!" << endl;
      return 0;
}

➜ clang main.cpp /bin/x86_64-unknown-linux-gnu-ld: /tmp/main-986467.o: in function main': main.cpp:(.text+0x11): undefined reference to std::cout'

➜ gcc main.cpp -o myProg /bin/ld: /tmp/ccJjbZYp.o: warning: relocation against _ZSt4cout' in read-only section .text' /bin/ld: /tmp/ccJjbZYp.o: in function main': main.cpp:(.text+0xe): undefined reference to std::cout'

Ted Lyngmo · Accepted Answer · 2021-04-26 11:52:57Z

1

The code compiles with gcc and clang - but since they are usually used to compile C programs, they do not link with the C++ standard library by default - so the linking phase fails.

You can link with a C++ standard library to confirm this.

Examples:

gcc main.cpp -lstdc++

clang main.cpp -stdlib=libc++ -lc++

edited Apr 26, 2021 at 11:52

answered Apr 26, 2021 at 11:45

Ted Lyngmo

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2 Comments

eamoc Over a year ago

Thanks for the answer, it makes sense now. i figured the file extension, and or the contents of the filew would lead gcc or clang to figure out that it was c++ code they were dealing with, but obviously not....

Ted Lyngmo Over a year ago

@eamoc You're welcome, and yes, as you've noticed, a file ending with .cpp will not make gcc or clang add the necessary libaries.

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