应对const char *类型变量的内容导致意外结果

Question

const char* mTest1; /*This variable has been assigned value before and 
                      the print out indicates it is correct.*/
char* mTest2;

if(mTest1 != NULL){
   mTest2 = new char[strlen(mTest1) +1]{};
   std::copy(mTest1, mTest1 + strlen(mTest1), mTest2);
   printf("\n===== mTest1 is: %s =============", mTest1);
   printf("\n===== mTest2 is: %s =============", mTest2);    
}

I would expect both of these two printf should print out the same result.

However, the result is not correct.

===== mTest1 is: c52b =============
===== mTest2 is: c52bZZZZ@m�� =============

Is there any wrong approach I've taken in coping the contents to mTest2?

Thanks

Answer 1

I am no expeert in c++ , but from this line

std::copy(mTest1, mTest1 + strlen(mTest1), mTest2);

It looks like you're missing to copy the null terminator in mTest2 . Maybe you can try

 std::copy(mTest1, mTest1 + strlen(mTest1) + 1 , mTest2);

Or, you can add that manually, after copying the string, using

mTest2[strlen(mTest1)] = '\0';

Answer 2

You forgot to add teminating symbol '\\0' at the end of the string after copying it:

const char* mTest1; /*This variable has been assigned value before and 
                      the print out indicates it is correct.*/
char* mTest2;

if(mTest1 != NULL){
   mTest2 = new char[strlen(mTest1) +1]{};
   std::copy(mTest1, mTest1 + strlen(mTest1), mTest2);
   mTest2[strlen(mTest1)] = '\0';
   printf("\n===== mTest1 is: %s =============", mTest1);
   printf("\n===== mTest2 is: %s =============", mTest2);    
}

When you work with c-style strings (char *), you always should remember about terminating symbols. As usual, copying operators copy only content of the string, and not terminating symbol, because it's signal for them to stop.