read an input file using vectors

Some parts of your code are almost certainly wrong. Other parts I'm less certain about -- they don't make much sense to me, but maybe I'm just missing something.

while(input_file) 

This is almost always a mistake. It won't sense the end of the file until after an attempt at reading from the file has failed. In a typical case, your loop will execute one more iteration than intended. What you probably want is something like:

while (input_file >> num_pins) 

This reads the data (or tries to, anyway) from the file, and exits the loop if that fails.

if (pins_.size() != num_pins) return false; 

This is less clear. It's not at all clear why we'd read num_pins from the file if we already know what value it needs to be (and the same seems to be true with width vs. wire.width).

for (size_t i = 1; i < file_name.size(); i=i+1) input_file>>cycles; 

This strikes me as the most puzzling part of all. What does the size of the string holding the file name have to do with anything? This has be fairly baffled.

I don't fully understand your code, but I don't see you are opening the input file anywhere. I think it should be:

std::ifstream input_file; evl_wire wire; int num_pins,width,cycles,no; std::vector<int>IP; input_file.open("name of the file"); if(input_file.is_open()) { while(input_file >> num_pins) //num_pins=2 { if (pins_.size() != num_pins) return false; for (size_t i = 0; i < pins_.size(); ++i) { input_file >> width;//width=1 for 1=0 ,=16 for i=2 if (wire.width != width) return false; pins_[i]->set_as_output(); } for (size_t i = 1; i < file_name.size(); i=i+1) input_file>>cycles; input_file>>no; pins_=IP; } input_file.close(); } 

The function I used:

bool input::validate_structural_semantics() { evl_wire wire; std::ifstream input_file;std::string line; int x[]={1000}; for (int line_no = 1; std::getline(input_file, line); ++line_no) std::string s; int i=0; std::istringstream iss; do { std::string sub; iss >> sub; x[i]=atoi(sub.c_str()); i++; } while (iss); if (pins_.size()!=x[0]) return false; for (size_t i = 0; i < pins_.size(); ++i) { if (wire.width != x[i+1]) return false; pins_[i]->set_as_input(); } for(size_t i=4;i<1000;i++) { for(size_t j=0;j<pins_.size();j++) pins_.assign(x[i-1],x[i+j]); } return true; } 

This implementation is using arrays but it didn't work,although there isn't any compling error.