I'd like to read a binary file and use something like std::string that automatically resizes the buffer and such.
I'm using Visual C++. What are my options?
views:
339answers:
5
+8
A:
The std::string class already does handle data with embedded NUL characters. What problem are you encountering?
Note that when using the .c_str() method, any embedded NUL character will terminate the returned C-style string.
Greg Hewgill
2009-10-07 21:38:12
Ah, problem I was having was using the `+=` operator to append a `char*` to the string. Best to use `.assign()` and `.append()`.
known
2009-10-08 01:23:13
What eaxactly do you mean with "any embedded NUL character will terminate the returned C-style string" ? .c_str() will return all characters of the `std::string`, and then an extra \0. It's not like .c_str() stops copying characters after the first \0. Of course, if you ONLY have that `const char*`, you won't know which \0 is the last one.
MSalters
2009-10-08 08:18:10
@MSalters: all the implementations of `std::string` that I'm familiar with don't actually copy anything on `.c_str()` (who would free it?). The problem is not `.c_str()` itself, but whatever function you pass it to next; for example `strlen()` would of course stop at the first NUL.
Greg Hewgill
2009-10-08 09:38:59
+4
A:
std::string should be safe to do so... you only have to be careful using .c_str() method. Use .data().
liori
2009-10-07 21:38:44
-1, you don't even know if the internal representation is in contiguous memory (depends on the implementation), so data() is very dangerous
orip
2009-11-19 15:46:26
Yes, I do (as long as the library is standards-compliant). C++ Standard, point 21.3.6.3: "If size() is nonzero, the member [data() const] returns a pointer to the initial element of an array whose first size() elements equal the corresponding elements of the string controlled by *this."
liori
2009-11-19 17:22:04
A:
std::string allows NUL characters so you can just go ahead and use that.
There is no problem with using c_str() or data(). Yes, the embedded NULs will be in your data, but if you don't use them to terminate your strings (you'll need to call length() to find out how many bytes are in your string) then all will be good.
R Samuel Klatchko
2009-10-07 21:42:01
+3
A:
You can always use std::vector<unsigned char> v (or whatever type of input you expect) and then to get at the buffer you simply &v[0] and v.size() for the size.
ezpz
2009-10-07 21:46:57
A:
Yes you can have embedded nulls in your std::string.
Example:
std::string s;
s.push_back('\0');
s.push_back('a');
assert(s.length() == 2);
Note: std::string's c_str() member will always append a null character to the returned char buffer; However, std::string's data() member may or may not append a null character to the returned char buffer.
Be careful of operator+=
One thing to look out for is to not use operator+= with a char* on the RHS. It will only add up until the null character.
For example:
std::string s = "hello";
s += "\0world";
assert(s.length() == 5);
The correct way:
std::string s = "hello";
s += std::string("\0world", 6);
assert(s.length() == 11);
Storing binary data more common to use std::vector
Generally it's more common to use std::vector to store arbitrary binary data.
std::vector<char> buf;
buf.resize(1024);
char *p = &buf.front();
It is probably more common since std::string's data() and c_str() members return const pointers so the memory is not modifiable. with &buf.front() you are free to modify the contents of the buffer directly.
Brian R. Bondy
2010-05-16 23:04:07