How to truncate a string array? C++ - c++

Question

Let's say I have a string array with 5 words and I want to only output the first 3 letters of each word. How do I go upon doing this? I know how to do it with one string but with an array of strings I get lost.
This is how to do it with one string
std::string test = "hello";
std::cout << test << std::endl;
test = test.substr(0,3);
std::cout << test << std::endl;
What I want to do is this
std::string test[5] = {"hello", "pumpkin", "friday", "snowboard", "snacks"};
I want to cout the first 3 letters of each word. I tried test[5] = test[5].substr(0,3); and that did not work.

Answer 1

test[5] doesn't work because you only have 5 items in your array, only indexes 0 to 4 are valid.
Generally with arrays you need to write a loop to go through each array item in turn, for instance
for (int i = 0; i < 5; ++i)
test[i] = test[i].substr(0,3);
for (int i = 0; i < 5; ++i)
cout << test[i] << endl;

Answer 2

With test[5] you are reading out of bounds thus invoking undefined behavior. Arrays in C++ are zero indexed so the last element would be test[4]. Create a function that utilizes for example the std::next function or string's substr member function. Call inside a range based loop:
#include <iostream>
#include <string>
void foo(const std::string& s) {
if (s.size() >= 3) {
std::cout << std::string(s.begin(), std::next(s.begin(), 3)) << '\n';
// or simply:
std::cout << s.substr(0, 3) << '\n';
}
}
int main() {
std::string test[5] = { "hello", "pumpkin", "friday", "snowboard", "snacks" };
for (const auto& el : test) {
foo(el);
}
}

Answer 3

test[5] = test[5].substr(0,3); won't work and more over you don't have `test[5]`, index starts from `0`.
you may want to do like this
for(int i=0 ; i<5; i++) {
test[i] = test[i].substr(0,3);
cout << test[i] << endl;
}

Answer 4

substr is what you are looking for. Here is my implementation.
#include <array>
#include <string>
#include <iostream>
int main () {
std::array<std::string,5> list {"hello", "pumpkin", "friday", "snowboard", "snacks"};
for (const auto &word : list){
std::cout << word << std::endl;
}
for (auto &word : list){
word = word.substr(0,3);
}
for (const auto &word : list){
std::cout << word << std::endl;
}
}

Answer 5

Use the standard library.
std::for_each(std::begin(test), std::end(test), [] (auto& s) { s.erase(3); });
Or even a simple range-based for loop:
for (auto&& s : test) {
s.erase(3); // Erase from index 3 to end of string.
}
Or maybe even create another container with views of the original strings:
auto test2 = std::accumulate(std::begin(test), std::end(test),
std::vector<std::string_view>{},
[] (auto& prev, std::string_view sv) -> decltype(prev)& {
prev.push_back(sv.substr(0, 3));
return prev;
});