Hippocamplus My Second Memory


File I/O

Read text file one line at a time

#include <fstream>

std::ifstream in_file('file.txt');
std::string line;
while(std::getline(in_file, line)){
    // Do something with 'line'

Data structures

std::vector<std::string> str_vec;
str_vec.push_back('one element');
for(unsigned int ii=0; ii<str_vec.size(); ii++){
    // LOOP ACTION on 'str_vec[ii]'

std::map<std::string,std::double> map_obj;
map_obj['key1'] = 1.3;
// check if a key is in the map
if(map_obj.count('key2') > 0)){
    // something with map_obj['key2'] ?
// iterate over key/value pairs
for(std::map<int,int>::iterator iter=map_obj.begin(); iter!=map_obj.end(); iter++){
    // iter->first contains the key
    // iter->secong contains the value

Maybe unordered_map is better for what I need in general?

String manipulation

  • .length()
  • convert to int: atoi(str_obj.c_str());
  • convert to double: atof(str_obj.c_str());
  • check for presence of a substring:str_obj.find("pattern") == std::string::npos
  • extract a substring: str_obj.substr(3, 7)
  • insert characters: str_obj.insert(10, "INSERT")

Split a string

std::vector<std::string> split_str(std::string in_str, std::string delim="\t"){
  std::vector<std::string> line_v;
  auto f_start = 0U;
  auto f_end = in_str.find(delim);
  while (f_end != std::string::npos)
      line_v.push_back(in_str.substr(f_start, f_end - f_start));
      f_start = f_end + delim.length();
      f_end = in_str.find(delim, f_start);
  line_v.push_back(in_str.substr(f_start, in_str.size()));
  return line_v;