String in C++

Summary

In this post, I will introduce the string class in c++ STL. It covers useful APIs and some of my recommendations.
1. Split
2. Access
3. Comparison
4. Numeric-Conversions

Details

Split

Thanks to this post, we present the conlusions for split first.
1. If you have access to boost, please do Solution 1.
2. You do not want to include other libraries. Implement own algorithms using Solution 2.
3. Use stream and see Solution 3.

Solutions

1. boost

#include <boost/algorithm/string.hpp>

std::string text = "Let me split this into words";
std::vector<std::string> results;

boost::split(results, text, [](char c){return c == ' ';});

Boost::split essentially performs multiple find_if on the string on the delimiter, until reaching the end.

It allows even several different delimiters and is 60% faster than solution 3.

2. getline

char delimiter = ',';
std::vector<std::string> tokens;
std::string token;
std::istringstream tokenStream(s);
while (std::getline(tokenStream, token, delimiter))
{
    tokens.push_back(token);
}

3. stream

std::string text = "Let me split this into words";

std::istringstream iss(text);
std::vector<std::string> results(std::istream_iterator<std::string>{iss},
                                 std::istream_iterator<std::string>()); // only works for space

Access

Actually string acts like vector<char>, we recommend you use .at() rather than [], since .at() check the boundary and throw exceptions.

string str = "hello";
cout << str.at(100) << endl; // libc++abi.dylib: terminating with uncaught exception of type std::out_of_range: basic_string
cout << str[100] << endl; // exit normally, print something you do not really know

Comparison

We can use != and == directly.

For < and >,

value	relation between compared string and comparing string
< 0	Either the value of the first character that does not match is lower in the compared string, or all compared characters match but the compared string is shorter.
> 0	Either the value of the first character that does not match is greater in the compared string, or all compared characters match but the compared string is longer.

"abc" < "abcd"; // true
"abc" < "bbc" ; // true

Numeric Conversions

The functions throw a std::invalid_argument exception if the conversion is not possible and a std::out_of_range exception if the determined value is too big for the destination.

#include <cfloat>
cout << INT_MAX << endl;
cout << DBL_MAX << endl;
cout << FLT_MAX << endl;
/*
2147483647
1.79769e+308
3.40282e+38
*/

Method	Description
std::to_string(val)	Converts val into a std::string.
std::stoi(str)	Returns an int value.
std::stol(str)	Returns a long value.
std::stoll(str)	Returns a long long value.
std::stoul(str)	Returns an unsigned long value.
std::stoull(str)	Returns an unsigned long long value.
std::stof(str)	Returns a float value.
std::stod(str)	Returns a double value.
std::stold(str)	Returns an long double value.