On 7/6/2010 1:26 PM, James Kanze wrote:
On Jul 6, 3:47 pm, "Peter Olcott"<NoS...@OCR4Screen.com> wrote:
http://groups.google.com/group/comp.lang.c++/msg/d27c88e57faadeb5?hl=en
Will the method specified in the above link always work
correctly for static binary files. (By static I mean that they
will not be written to while they are being read).
It's not guaranteed by the standard, and there have been systems
where it wouldn't work. As long as the file is opened in binary
mode, and doesn't change, it will probably work with most
implementations under Windows or Unix (where the system does
maintain file position as a byte count, rather than some other
representation). There are almost certainly mainframes and
legacy systems, however, where it won't work.
--
James Kanze
I adapted your code to my style making minor formatting changes and tested
it on several files. It worked perfectly. What I liked best about your
code is that it taught me a very simple way to use exceptions.
I had previously avoided exceptions because their typical implementation
was far too convoluted, and I always strive for the simplest possible
code. Now that I know how to throw and catch text based exceptions they
are very simple. That was the cleanest error handling that I have ever
seen. This will become my new idiom for file processing and error
handling.
#include <iostream>
#include <fstream>
#include <vector>
void readAll(char const* filename, std::vector< char >& data ) {
std::ifstream fin;
fin.open(filename, std::ios_base::in | std::ios_base::binary);
if ( ! fin )
throw "cannot open";
fin.seekg( 0, std::ios::end );
if ( ! fin )
throw "seek error";
long long size = fin.tellg();
std::cout << filename << ": size = " << size << std::endl ;
if ( size != 0 ) {
fin.clear() ;
fin.seekg( 0, std::ios::beg );
if ( ! fin )
throw "rewind failed";
data.resize( size );
fin.read( &data[ 0 ], size );
if ( ! fin )
throw "read failed";
}
}
int main( int argc, char** argv ) {
std::vector< char > data;
if (argc == 2)
try {
readAll( argv[ 1 ], data );
} catch ( char const* error ) {
std::cout << argv[ 1 ] << ": " << error << std::endl ;
}
else
std::cout << "Must specify a FileName!" << std::endl ;
return 0;
}
in catch blocks. Throw a unique type (preferably derived from something
from <stdexcept>) instead. std::exception has a virtual what() member