C++ :: How To Calculate Index Section For Document

Im problem with parsing. I read file line by line and i store another class bu when i parse the line last word gone example "I study algebra and discrite math" math didnt store.Why ? i want to calculate index section for document how can i solve this problem??

Code:

void DocumentIndex::parse(){
size_t pos = 0; //position
pos =line.find(" ");
while( ( pos = line.find(" ") ) != std::string::npos )
{

[code]....