Strange behaviour of the typeid operator?

Question

Using XCode 3.2.3 (64-bit), I get following strange output. What am I doing wrong?

#include <iostream>
#include <typeinfo>

struct student {

};

int main()  
{  
    int i;
    student obj;

    std::cout << typeid(i).name() << "\n";
    std::cout << typeid(obj).name() << "\n";

    return 0;
}

Output:

i  
7student

type of the passing parameter to `typeid` as output. ie `int student` http://stackoverflow.com/questions/81870/print-variable-type-in-c — Mahesh, Jan 10 '11 at 00:10
possible duplicate of [Why typeid.name() returns weird characters using gcc?](http://stackoverflow.com/questions/4465872/why-typeid-name-returns-weird-characters-using-gcc) — Martin York, Jan 10 '11 at 00:57

templatetypedef · Answer 1 · 2020-04-17T03:59:34.957

The name() member function of the type_info struct is implementation-specific. There's no guarantee whatsoever that it will try to return something that matches what it says in the original program. In fact, the C++ ISO standard (18.5.1.7) actually says that this function returns "an implementation-defined NTBS" (null-terminated byte string). If it wanted to, it could have this always return the string "neener neerer I won't tell you the name of this type." This contrasts with Java's Class<?> type, which has very strict restrictions on what it can and cannot return.

If you’d like to convert the name from std::type_info into something more human, readable, check this other question for details.

score 4 · Accepted Answer · answered Jan 10 '11 at 00:08

What's going on is nothing special. Just that typeid doesn't promise to return the "original" name of the type, but just a name.

The function returns an implementation-defined string, which, if you're lucky, is recognizable, but it makes no promise of that.

Strange behaviour of the typeid operator?

2 Answers2

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