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Asked: 2026-06-10T17:52:30+00:00

I attended a session in which it was taught that we should not use

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I attended a session in which it was taught that we should not use "using namespace std", instead do "std::cout" for using some call of the std namespace as this shall increase size of the binary

I tried verifying the same with the following experiment. The code & its output is as follows:-

    [Fooo@EXP]$ cat namespacestd.cpp
    #include<iostream>

    #ifdef STD
            using namespace std;
    #endif

    int main()
    {
    #ifndef STD
            std::cout<<"\n ==> Workign \n";
    #else
            cout<<"\n ==> Workign \n";
    #endif

    return 0;

    }


    [Fooo@EXP]$ time g++ -c namespacestd.cpp -DSTD

    real    0m0.246s
    user    0m0.215s
    sys     0m0.030s
    [Fooo@EXP]$ size namespacestd.o
       text    data     bss     dec     hex filename
        310       8       1     319     13f namespacestd.o  
    [Fooo@EXP]$ time g++ -c namespacestd.cpp

    real    0m0.258s
    user    0m0.224s
    sys     0m0.034s
    [Fooo@EXP]$ size namespacestd.o
       text    data     bss     dec     hex filename
        310       8       1     319     13f namespacestd.o

    [Fooo@EXP]$ time g++ -o namespacestd namespacestd.cpp -DSTD

    real    0m0.293s
    user    0m0.251s
    sys     0m0.042s
    [Fooo@EXP]$ size namespacestd
       text    data     bss     dec     hex filename
       1980     580     288    2848     b20 namespacestd
    [Fooo@EXP]$ time g++ -o namespacestd namespacestd.cpp

    real    0m0.274s
    user    0m0.239s
    sys     0m0.035s
    [Fooo@EXP]$ size namespacestd
       text    data     bss     dec     hex filename
       1980     580     288    2848     b20 namespacestd
    [Fooo@EXP]$

As I see from my experiment that

there is no effect on the size of binary

only

there is a difference in the compilation time.

Kindly correct me if my conclusions are flawed

Thanks

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1 Answer

  1. Editorial Team

    using namespace std shouldn’t affect binary size with most compilers. It should still be avoided for another reason:

    The namespace std is really big. There are literally thousands of identifier in there which are all in the scope of your program. This increases the likeliness of collisions with your own identifiers or identifiers from other libraries which can cause some nasty surprises.

    See also this related question: Why is "using namespace std" considered bad practice?

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