Get file section

[nathanf534]

I am creating a program that sends a file quickly by sending sections of it in datagrams....
everything is working fine so far, except when i use file.read(buffer,size)
size is always 40000, but the size of buffer is a seemingly random number everytime, about 100-200 in length. I have allocated enough memory for buffer, and the file it is reading from is very large (around 200mb) so i know its not at the end of the file. What could be wrong? If you need any of the code, just ask for it

[helios]

Did you open the file as binary? If you didn't, it's likely that a newline conversion is happening in the back.

[nathanf534]

yes, i did open it as binary, but it still doesn't work. It does correctly get newline characters
here is the code im using to get a section of the file

void getSection(int section,char* data){
    inputFile.seekg(getSectionStart(section),ios::beg);
    clearChar(data);
    strncpy(data,getBlankHeader(header),header);
    inputFile.read(data+header,getSectionLength(section));
    cout<<strlen(data+header)<<endl;
    _memccpy(data+(header-getDecPlaces(section)),intToChar(section),NULL,getDecPlaces(section));
}
void clearChar(char* c){
strncpy(c,"",strlen(c));     
}

this function returns a char* with a header 8 characters long, then a portion of the file, 40000 characters long. It works on a text file, with any possible character you can type on a keyboard, but then i tried to send a .avi file, and it doens't return something 40000 long anymore, but some random length.

[helios]

Why are you using strlen() to get the length of the read buffer if you're getting binary data, which you don't know where it could contain a '\0'?
As far as I know, the only way to know how many bytes were read is by checking the file pointer position after the call to read and subtracting with the position before the call.

[nathanf534]

hmm.. thats a good point, ill look into this
how could i send binary data through a datagram then? doesn't it take a null terminated string as input?

[helios]

Base64 is a method to encode binary data as ASCII.
http://en.wikipedia.org/wiki/Base64

[nathanf534]

ahhhh... nevermind. I looked further into my code, and i found that for the string length parameter on the sendto function, i used strlen. I just changed this to my own function to get the length, and its fine
EDIT: nevermind, i still need a little help...
so i sent 40000 characters throught a datagram (i hope it was 40000, but there isnt anyway i can make sure, except the length was set to 40000)
then, the client recieves the packet... and saves it to a file opened as binary with... file<<buffer;
but wouldn't that only save until it reaches \0? so how could i get it to save the whole thing of length 40000?
EDIT: wow.. i just remembered after i posted this. file.write(buffer,length); anyway this works, so thanks helios for your help. :D

[helios]

If only every poster was like you...