CODEWITHSUNDEEP
c++stringc++11ascii
Humam Helfawi
Humam Helfawi

Reputation: 20264

Is std::string supposed to have only Ascii characters?

Is std::string supposed to hold a set of characters in Ascii encoding on all platforms and standard compilers?

In other words, can I be sure that my C++ program will get a set of Ascii characters if I do this:

std::string input;
std::getline(std::cin, input);

EDIT:

In more accurate words, I want to make sure that if the user enter "a0" I will get a std::string with two elements. The first one is 97 and the second is 48

Upvotes: 5

Views: 6539

Answers (3)

πάντα ῥεῖ
πάντα ῥεῖ

Reputation: 1

In other words, can I be sure that my C++ program will get a set of Ascii characters if I do this ...

No. std::string is actually a specialization for std::basic_string<>, like
using std::string std::basic_string<char>;:

template< 
    class CharT, 
    class Traits = std::char_traits<CharT>, 
    class Allocator = std::allocator<CharT>
> class basic_string;

and can hold any type of character that is defined with Traits.

In short std::string can contain ASCII character encodings, as well as EBCDIC, or any others. But it should be transparent as how you're using it.

Upvotes: 3

Lightness Races in Orbit
Lightness Races in Orbit

Reputation: 385144

No. std::string does not hold "characters"; it holds bytes.

Those bytes could form some human-readable string through encoding as ASCII or EDBCIC or Unicode. They could be a binary encoding storing computer-readable information (e.g. a JPEG image). They could be guidelines from aliens on how to use Stack Overflow for three weeks straight without being downvoted even once. They could be total random white noise.

Your program needs to be made to understand what the data it is reading actually means, and how it is encoded. This shall be part of your task as the programmer.

(It's unfortunate, and nowadays misleading, that char is named char.)

Upvotes: 10

R Sahu
R Sahu

Reputation: 206577

No, there is no guarantee that

std::string input;
std::getline(std::cin, input);

will return only ASCII characters. The range of values that be held by a char is not limited to the ASCII characters.

If your platform uses different encoding than ASCII, you'll obviously get a different set of characters.

Even if your platform uses ASCII encoding, if char on the platform is an unsigned type, than it can very easily hold the extended ASCII characters too.

Upvotes: 3

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