C++: How to make function return only strings which are a part of a list?

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I want my function to return a string, but only strings which are a member of a specific list/set of strings. How can I go about doing this?

You do not want to return a string, you want to return a string that has an additional restriction (being part of some predefined set).

For that you'd need a new type:

class BusinessStringWrapper {
public:
  BusinessStringWrapper(std::string arg): value{arg} {
    if (/* arg is not ok */) {
      throw;
    }
  }
  // you can replace that with factory method
  // can also return std::optional instead of throwing if the condition is not met
  // that depends on your application

  std::string value() const { return value; }

private:
  const std::string value;
};

And in your application you'd operate on this type, accessing value if needed.

how to return a string array from a function, Sign up or log in to view your list. A string array in C can be used either with char** or with char*[] . If you want to return the string array, you have to reserve it dynamically: To programmers just starting out, the concept of a "stack" or the "​heap" might be a little confusing, especially if you have started programming in a​  The C standard library provides numerous built-in functions that your program can call. For example, strcat () to concatenate two strings, memcpy () to copy one memory location to another location, and many more functions. A function can also be referred as a method or a sub-routine or a procedure, etc.

Hoe about using a std::set<std::string>?

#include <iostream>
#include <set>
#include <string>

std::string helper(const std::string & str,
                   const std::set<std::string> & lst)
{
    return lst.find(str) == lst.end() ? "" : str;
}

int main()
{
    std::set<std::string> lst = {"alpha", "beta", "gamma"};
    std::cout << "return " << helper("alpha", lst) << "\n";
    std::cout << "return " << helper("zeta", lst) << "\n";

    return 0;
}

Output

return alpha
return

Of course, it really depends on what your definition of does not return is.

If it means an empty string, then use the above solution. Keep your life simple.

If it means an error and the program should terminate, you may #include <cassert> and just

assert(lst.find(str) != lst.end());

If it means an exception to handle, you may try throw and catch.

If it means returning a std::string if str is in a predefined list, but a void if it's not, then you may need some tricks as described in <type_traits>.

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You can do this std::map<CardType, std::string> in the example below, or use std::map<int, std::string> to associate a string with any integer. For example mp[123]="abcd"

#include <iostream>
#include <string>
#include <map>

enum CardType {
    SPADE,
    HEART,
    CLUBS,
    DIAMD
};

std::map<CardType, std::string> mp{ 
    {CardType::SPADE, "Spade"},
    {CardType::HEART, "Heart"},
    {CardType::CLUBS, "Clubs"},
    {CardType::DIAMD, "Diamond"}
};

int main()
{
    std::cout << mp[CardType::SPADE] << std::endl;
    return 0;
}

11. Lists, The values that make up a list are called its elements, or its items. We will use the The following list contains a string, a float, an integer, and (amazingly) another list: The function len returns the length of a list, which is equal to the number of its elements. a = [1, 2, 3] >>> b = [4, 5, 6] >>> c = a + b >>> c [1, 2, 3, 4, 5, 6]. strrchr: The strrchr() function in C/C++ locates the last occurrence of a character in a string. It returns a pointer to the last occurrence in the string. The terminating null character is considered part of the C string. Therefore, it can also be located to retrieve a pointer to the end of a string. It is defined in cstring header file. Syntax :

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Lists, In a string, the values are characters; in a list, they can be any type. If you try to read or write an element that does not exist, you get an IndexError. This loop traverses the list and updates each element. len returns the number of elements in the list. The sum() function only works when the list elements are numbers. A function in C can be called either with arguments or without arguments. These function may or may not return values to the calling functions. All C functions can be called either with arguments or without arguments in a C program. Also, they may or may not return any values. Hence the function prototype of a function in C is as below:

[PDF] The strchr() function finds the first occurrence of a specified , When strchr() finds the character, it returns a pointer to that character. Knowing look for the string str2, but only the characters it contains. The final, and perhaps most useful, C string-searching function is strstr(). Table lists the complete set of isxxxx() You can do many interesting things with the character-​test macros. There are two ways to return strings that won't barf so readily. returning buffers (static or dynamically allocated) that live for a while. In C++ use 'helper classes' (for example, std::string) to handle the longevity of data (which requires changing the function's return value), or; pass a buffer to the function that gets filled in with information.

Comments
  • Why do you need the enum to be strings in 1st place? If you want to display the values, provide a simple function to map those values to readable strings.And in fact you could use a std::map<CardType,std::string> to make that as easy as possible.