Why is sizeof (Str. substr (0, 3). c_str () = 8?

Translated from stackoverflow, an interesting question.

Problem:

 
StringSTR ="Abcdefgdcb"; Cout<Sizeof(Str. substr (0,3). C_str ());
 

For some reason, the above string is giving me 8. I assumed c_str () returns a null string,
For some reason, the result of the above string is 8. I estimate that c_str () returns a null value,

And sizeof uses the null to determine the size of the string.
And the sizeof function uses this null to define the size of this string.

Answer:
Because sizeof doesn't give you the length of a string,
Because sizeof does not give you the length of a string,

It gives you the size of the type (const char * in this case). Try strlen.
He gave you the size of this type (in this case, the type is the const char * type returned by c_str (). To get the correct result, try the strlen function.

On your system, sizeof (const char *) = 8, like any other pointer.
In your system, sizeof (const char *) = 8, the same as all other pointer types.

8 is the size of a pointer on your machine (64-bit)
8 is the size of a pointer on your 64-bit computer

There's your problem. sizeof tells you the size of a variable,
Do not assume that sizeof tells you the size of a variable,

Which has nothing to do with the value inside the variable, ever.
He will not make any changes to the variable in the variable .. Never.

Problem: http://stackoverflow.com/q/10668764/764869