Undefined reference to std::cout [FIXED]

In this article, we have present the reason behind the error "Undefined reference to std::cout" and different approaches to fix this error.

Table of contents:

1. Reason behind the error
2. Fix 1: Compile with g++ or clang++
3. Fix 2: Add header file
4. Fix 3: For Microsoft's compiler MSVC
5. Fix 4: Fix GCC/ G++/ Clang build

Reason behind the error

On compiling a C++ program, you may face this compilation error:

code.cpp:(.text+0x3d): undefined reference to 'std::cout'

This comes from the line:

std::cout << data << std::endl;

The reason is that the compiler is unable to find where the function cout has been defined. This is a standard C++ function.

Make sure you are working on a C++ code (not on a C code).

Fix 1: Compile with g++ or clang++

The most common problem is that you are trying to compile a C++ program with a C compiler such as gcc or clang. To compile a C++ program, we need a C++ compiler such as g++ or clang++.

If you need to use gcc, add this explicit flag -lstdc++ to include C++ standard libraries which are included automatically with g++.

gcc -lstdc++ code.c

If you are using gcc in a cmake file, use the following within cmake:

-DCMAKE_EXE_LINKER_FLAGS="-lstdc++"

The overall compilation command will be same. Just replace gcc with g++ or clang with clang++.

cout is a feature in C++ only.

g++ code.cpp
// OR
clang++ code.cpp

Fix 2: Add header file

Add this at the top of your C++ program if you missed:

#include <iostream>
using namespace std;

Compile your C++ program and the error should be fixed.

Fix 3: For Microsoft's compiler MSVC

If you are using MSVC, include the following header files:

#include "stdafx.h"
#include <iostream>

Note the order is important. This should fix the issue.

Fix 4: Fix GCC/ G++/ Clang build

If the other fixes have not worked, it is highly likely that your GCC compiler installation is broken.

The suggestion is to build GCC/G++ from source so that the compiler installation is successful and you can compile your C++ code.

With the fixes in this article at OpenGenus, this issue of "Undefined reference to std::cout" should be fixed now. Continue your development work.