single character c-style string full of junk

It's a shame I can't figure out such basic thing about c++, but c-style strings are acting as I wouldn't expect. For example, I create it like this: char* cstr = new char[1];

It's initialized to: Íýýýýý««««««««îţ . Like normal, I can set just first char because others are not really existing (or I thought that they aren't). While working whit c-style strings all this junk is ingored and everything works fine.

Now I mixed std::string whit those c-stlye one and what I get is a mess. Whit this code:

std::string str = "aaa";

str += cstr;

I end up whit: aaaÍýýýýý««««««««îţ , but now those characters actually exist as string.size() returns length including this junk.

I can't find why is this happening, but it must be connected whit string creating, because something like char* cstr = "aaa" results in aaa without any additional junk, but trying开发者_JAVA技巧 to change string initialized this way results in memory access violation. Could someone explain me this behavior please? Thanks!

PS: My JavaScript Failed to load so if someone could format this post properly, I'd be glad!

Answer: Oh god! How could I forget on that... thanks to all for, well, immediate answer. Best one was from minitech so I'll mark this as answer as soon as my java script loads up :/

All C-style strings are null-terminated. So, a string initialized using new char[1] leaves you space for no characters. You can't set the first character to anything but \0, otherwise normal string operations will keep reading into memory until they find a zero. So use new char[2] instead.

When working with C-style strings you need to have a null terminator:

char* cstr = new char[2];
cstr[0] = 'X';
cstr[1] = '\0';

Having said all that, it is really bad code to do the above. Just use std::string unless you have a very good reason not too. It takes care of the memory allocations and deallocations for you.

C-style strings require a NUL ('\0') terminator; they don't have a length associated with them like C++ strings do. So your single-character string must be new char[2]; it will not be initialized; and you will need to make sure it's terminated with \0.

When you use new char[1], you request space for an array of characters. There is no request that said characters are initialized. Thus, the "junk" that you see is uninitialized memory. Before treating the array as a C-style string, you should do this:

cstr[0] = '\0';

c-style strings are NULL delimited. So, to ignore any junk in memory you need to place NULL byte('\0') in the string body. Otherwise, system library function will look at all bytes starting with your string start until they meet NULL byte in the memory (which will be at some random position).

This also mean that to have c-style string of one character you actually need to allocate 2 bytes: one for a meaningful character and second for '\0'.