Recently I have found a lot of examples, most of them regards the C++ 98, anyways I have created my simple-array and a loop (codepad):
#include <iostream>
using namespace std;
int main ()
{
string texts[] = {"Apple", "Banana", "Orange"};
for( unsigned int a = 0; a < sizeof(texts); a = a + 1 )
{
cout << "value of a: " << texts[a] << endl;
}
return 0;
}
Output:
value of a: Apple value of a: Banana value of a: Orange Segmentation fault
It's working fine, except the segmentation fault at the end.
My question is, does this array/loop through is done a good way? I am using C++ 11 so would like to be sure it fits the standards and couldnt be done a better way?
You can do it as follow:
#include < iostream >
using namespace std;
int main () {
string texts[] = {"Apple", "Banana", "Orange"};
for( unsigned int a = 0; a < sizeof(texts) / 32; a++ ) { // 32 is the size of string data type
cout << "value of a: " << texts[a] << endl;
}
return 0;
}
Add a stopping value to the array:
#include <iostream>
using namespace std;
int main ()
{
string texts[] = {"Apple", "Banana", "Orange", ""};
for( unsigned int a = 0; texts[a].length(); a = a + 1 )
{
cout << "value of a: " << texts[a] << endl;
}
return 0;
}
string texts[] = {"Apple", "Banana", "Orange"};
for( unsigned int a = 0; a < sizeof(texts); a = a + 1 )
{
cout << "value of a: " << texts[a] << endl;
}
Nope. Totally a wrong way of iterating through an array. sizeof(texts)
is not equal to the number of elements in the array!
The modern, C++11 ways would be to:
std::array
if you want an array whose size is known at compile-time; orstd::vector
if its size depends on runtimeThen use range-for when iterating.
#include <iostream>
#include <array>
int main() {
std::array<std::string, 3> texts = {"Apple", "Banana", "Orange"};
// ^ An array of 3 elements with the type std::string
for(const auto& text : texts) { // Range-for!
std::cout << text << std::endl;
}
}
You may ask, how is std::array
better than the ol' C array? The answer is that it has the additional safety and features of other standard library containers, mostly closely resembling std::vector
. Further, The answer is that it doesn't have the quirks of decaying to pointers and thus losing type information, which, once you lose the original array type, you can't use range-for or std::begin/end
on it.
you need to understand difference between std::array::size and sizeof() operator. if you want loop to array elements in conventional way then you could use std::array::size. this will return number of elements in array but if you keen to use C++11 then prefer below code
for(const string &text : texts)
cout << "value of text: " << text << endl;
sizeof(texts)
on my system evaluated to 96: the number of bytes required for the array and its string instances.
As mentioned elsewhere, the sizeof(texts)/sizeof(texts[0])
would give the value of 3 you were expecting.
How about:
#include <iostream>
#include <array>
#include <algorithm>
int main ()
{
std::array<std::string, 3> text = {"Apple", "Banana", "Orange"};
std::for_each(text.begin(), text.end(), [](std::string &string){ std::cout << string << "\n"; });
return 0;
}
Compiles and works with C++ 11 and has no 'raw' looping :)
If you have a very short list of elements you would like to handle, you could use the std::initializer_list introduced in C++11 together with auto:
#include <iostream>
int main(int, char*[])
{
for(const auto& ext : { ".slice", ".socket", ".service", ".target" })
std::cout << "Handling *" << ext << " systemd files" << std::endl;
return 0;
}
sizeof
tells you the size of a thing, not the number of elements in it. A more C++11 way to do what you are doing would be:
#include <array>
#include <string>
#include <iostream>
int main()
{
std::array<std::string, 3> texts { "Apple", "Banana", "Orange" };
for (auto& text : texts) {
std::cout << text << '\n';
}
return 0;
}
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Source: Stackoverflow.com