c++ - Strange Pointer Behavior -

take following struct , class:

struct teststruct { };  class testclass { public:     teststruct* teststruct; }; 

do following in main:

testclass testclass; if (testclass.teststruct == null)     cout << "it null." << endl; else     cout << "it not null."; 

the output be: it not null..

however, if instead this:

testclass testclass; if (testclass.teststruct == null)     cout << "it null." << endl; else     cout << "it not null." << endl << testclass.teststruct; 

the output be: it null..

interestingly enough, if (fundamentally same above):

testclass testclass; if (testclass.teststruct == null) {     cout << "it null." << endl; } else {     cout << "it not null." << endl;     cout << testclass.teststruct; } 

the output be:

it not null. 0x7fffee043580. 

what going on?

your pointer not initialized when declare testclass. experience here undefined behaviour. value of pointer last value contain in memory section stored.

if wanted always null, need initialize in constructor of class.

class testclass { public:     testclass(): teststruct(null) {}     teststruct* teststruct; };