parse an unknown size string

Question

I am trying to read an unknown size string from a text file and I used this code :

ifstream inp_file;
char line[1000] ;
inp_file.getline(line, 1000);

but I don't like it because it has a limit (even I know it's very hard to exceed this limit)but I want to implement a better code which reallocates according to the size of the coming string .

Answer 1

The following are some of the available options:

istream& getline ( istream& is, string& str, char delim );
istream& getline ( istream& is, string& str );

Answer 2

One of the usual idioms for reading unknown-size inputs is to read a chunk of known size inside a loop, check for the presence of more input (i.e. verify that you are not at the end of the line/file/region of interest), and extend the size of your buffer. While the getline primitives may be appropriate for you, this is a very general pattern for many tasks in languages where allocation of storage is left up to the programmer.

Answer 3

Maybe you could look at using re2c which is a flexible scanner for parsing the input stream? In that way you can pull in any sized input line without having to know in advance... for example using a regex notation

^.+$

once captured by re2c you can then determine how much memory to allocate...

Answer 4

Have a look on memory-mapped files in boost::iostreams.