getline() special...

Reply to getline() special... on Mon, 26 Feb 2007 08:05:38 GMT

FightingWolf — Mon, 26 Feb 2007 08:05:38 GMT

Hey,

I found something special in the getline() function, I don't understand.

If I use the getline function in case of an Excel-sheet or an image - to get the image-data - the getline function breakes after a NULL termination ( \0 )

fstream oFile_e;

oFile_e.open("BAB.xls",ios::in);

oFile_e.getline(chTest, 100,'\n');

BAB.xls containes the \0 from position 9 to 12

chTest is after the getline function only filled up to position 9 ( after the first \0 )

--> no problem with the ios::binary mode. With this mode it's possible to read the whole data.

But if I write out some chars in a file and some of them are \0, I can read the whole data WITHOUT the ios::binary mode.

Do you understand that phenomenon?

Reply to getline() special... on Mon, 26 Feb 2007 08:15:35 GMT

CStoll — Mon, 26 Feb 2007 08:15:35 GMT

getline() still reads the whole line of your file, but you use it as a C-string (char-array) afterwards. And from C's point of view, the character '\0' marks the end of a string, so any access through C functions would only result in the part before the first '\0' mark.

The best solution would be using the class std::string an the global function getline() instead of the istream member. Or you could use the method 'gcount()' to find out the real length of the read string.

Reply to getline() special... on Mon, 26 Feb 2007 13:27:21 GMT

FightingWolf — Mon, 26 Feb 2007 13:27:21 GMT

thx for the answer but I think you don't understand what I mean. If i use the ios::binary mode in the getline function it works, too. But I don't understand why this funcion breakes ( stops ) reading when I read out image data, and an other time it continues ( when I write the data myself into an file with \0 ).

for example:

the image data: abcde\0\0\0\0cdf\0\0a
the data I wrote into a file: abc\0\0\0a

now I read out both data with the same function and the same values / attributes.

So why fills the getline function my array compleately to the last char ( a ) at my own data and not only to the first \0 mark like in the image data?

Both files containes \0. One time I have an return of the function ( own data in an array: abc\0\0\0a ), one time not ( Image data in an array: abcde\0\0\0\0cdf\0\0a ).

So look... I don't have any problems to read out any data from an file, but im interested in this phenomenon.