I have question about output in console
string str;
scanf("%s", str);
printf("%s", str);
Why do I get strange symbols, which have trouble with encoding?
2 Answers
std::string is a class (user-defined type). On the other hand, the conversion specifier s is designed to input or output character arrays. So the code snippet has undefined behavior.
Instead you could use operators >> and << overloaded for the class std::string to input or output data from/to streams like
std::string str;
std::cin >> str;
std::cout << str << '\n';
If you want to use the functions scanf and printf then use character arrays as for example
char str[100];
scanf( "%99s", str );
printf( "%s\n", str );
If as you wrote in a comment
I have a task, out string with help printf.
then in this case you should check whether string is indeed the standard C++ type or an alias for the type char * introduced like for example
typedef char *string;
or like
using string = char *;
5 Comments
Nikolay
I have a task, out string with help printf. Do you know how do it?
Vlad from Moscow
@user18999150 You shall not use objects of the type std::string with scanf or printf though there is a possibility to output an object of the type std::string using printf for example the following way printf( "%s\n", str.c_str() ); or printf( "%s\n", str.data() );
πάντα ῥεῖ
@Klaus nitpick than isn't the same as then.
Vlad from Moscow
@user18999150 I suspect that they mean an alias of the type char * as I wrote in my answer.:) Or they just refer to C strings using the word string.
πάντα ῥεῖ
@Klaus it's not a "stupid task" at all. It makes you familiar how to interact with legacy c-libraries you cannot change, and have to use these in your daily, bread and butter, payed real world production code.
printf and scanf expect variables of type [const] char * with an "%s" format specifier.
In general, the other answer to use std::cin / std::cout instead is preferrable.
If you absolutely must use printf to output a std::string, use the c_str() method to get access to a const char * representing the same string as in the std::string; example:
string str;
std::cin >> str;
printf("%s", str.c_str());
Note the const in const char* c_str() - meaning you are not allowed to change the returned string. So, it cannot be used for scanf. There, you'd have to stick to a char *...
1 Comment
Klaus
In such an answer I expect at minimum that such coding should be avoided! Use C or C++... If someone gives such a task... there must be a very good reason for this! Teaching bad style should not be one of them...
printfexpect a c string i.e.char*? Same withscanf. Also why useprintfandscanfinsteadstd::coutandstd::cin?