Binary vs. formatted std::string reading/writing to streams

[Leslaw Bieniasz]

Hi,

I need to write and read std::strings as whole objects
from/to std::streams, either in a formatted or binary way.
Are there any built-in mechanisms for doing this (any global
functions or class methods in std::string)?
I cannot find any.

Formatted writing seems easy, for example:

std:stream outstr;
std::string str;
outstr << str;

outputs entire str to outstr. However, something like

std::instream instr;
std::string str;
instr >> str;

gets only the first continuous sub-string contained in
instr into str. The sub-string may not be identical to
the entire string that was earlier written to the stream
from which the reading is performed.

What I need is a possibility to save an std::string into a stream/file
and then re-read the entire string from the same stream/file,
even if the string contained separate sub-strings.
Perhaps some sort of binary reading/writing can be applied?

A related question is:

Is this legal to open streams in binary mode, and use operators
<< and >> to read or write from these streams? For example,
if I open a binary stream, can I save (and later correctly retrieve)
some objects in it using binary writing, and some other objects using
formatted writing employing operators << and >> ?

Leslaw

 

[Eric Böse-Wolf]

Hi Leslaw,

gets only the first continuous sub-string contained in
instr into str. The sub-string may not be identical to
the entire string that was earlier written to the stream
from which the reading is performed.

What do you mean by "substring"? Are "substrings" delimited by
whitespace? Then you might take a look at:

http://www.cplusplus.com/reference/iostream/manipulators/noskipws/

Yours sincerely,

Eric

 

[Thomas J. Gritzan]

Am 15.01.2010 11:42, schrieb Leslaw Bieniasz:

I need to write and read std::strings as whole objects
from/to std::streams, either in a formatted or binary way.
Are there any built-in mechanisms for doing this (any global
functions or class methods in std::string)?
I cannot find any.

Formatted writing seems easy, for example:

std:stream outstr;
std::string str;
outstr << str;

outputs entire str to outstr. However, something like

std::instream instr;
std::string str;
instr >> str;

gets only the first continuous sub-string contained in
instr into str.

nistr >> str; stop reads until it finds a whitespace.

If you want to read a line of text, use std::getline:

std::getline(instr, str);

This function reads until it find a '\n' character in the stream. For
another delimiter, there's also a three argument version of that
function where the third parameter is the delimiter:
http://www.cplusplus.com/reference/string/getline/