How to use the basic_string::find_first_of () STL functions in Visual C++

MORE INFORMATION

Required header

   <xstring>

Prototype

   size_type find_first_of(const basic_string& _X, size_type iPos = 0);
   size_type find_first_of(const element_type *_S, size_type iPos,

                           size_type cElementsIn_S);

   size_type find_first_of(const element_type *_S, size_type iPos = 0);
   size_type find_first_of(element_type _C, size_type iPos = 0);

Note The class/parameter names in the prototype may not match the version in the header file. Some have been modified to improve readability.

Description

The member functions each find the first (lowest position) element of the controlled sequence at or after position iPos that matches any of the elements in the operand sequence specified by the remaining operands. If it succeeds, it returns the position. Otherwise, the function returns npos.

The position returned is 0 (zero) based. The npos return value is a special value indicating that none of the elements were found.

Sample code

////////////////////////////////////////////////////////////////////// 
// 
// Compile options needed: /GX
// 
// main.cpp : Demonstrates the use of the basic_string::find_first_of().
// 
// Functions:
// 
//    basic_string::find_first_of() - find the first instance in the
//         controlled string of any of the elements specified by the
//         parameters. The search begins at an optionally-supplied
//         position in the controlled string.
// 
// Written by Michael Reeves
// of Microsoft Product Support Services,
// Copyright (c) 1996 Microsoft Corporation. All rights reserved.
////////////////////////////////////////////////////////////////////// 

#include <xstring>
#include <iostream>

#if _MSC_VER > 1020   // if VC++ version is > 4.2
   using namespace std;  // std c++ libs implemented in std
   #endif

typedef basic_string<char, char_traits<char>,
             allocator<char> > test_string;

void main()

{

    test_string str1("Heartbeat");
    test_string str2("abcde");
    int iPos = 0;

    cout << "The string to search is '" << str1.c_str() << "'"
         << endl;

    // find the first instance in str1 of any characters in str2
    iPos = str1.find_first_of (str2, 0);  // 0 is default position

    cout << "Element in '" << str2.c_str() << "' found at position "
         << iPos << endl;

    // start looking in the third position...
    iPos = str1.find_first_of (str2, 2);

    cout << "Element in '" << str2.c_str() << "' found at position "
         << iPos << endl;

    // use an array of the element type as the set of elements to
    // search for; look for anything after the fourth position
    char achVowels[] = {'a', 'e', 'i', 'o', 'u'};
    iPos = str1.find_first_of (achVowels, 4, sizeof(achVowels));


    cout << "Element in '";
    for (int i = 0; i < sizeof (achVowels); i++)
        cout << achVowels[i];
    cout << "' found at position " << iPos << endl;

    // use a string literal to specify the set of elements
    char szVowels[] = "aeiou";
    iPos = str1.find_first_of (szVowels, 0);  // 0 is default position

    cout << "Element in '" << szVowels << "' found at position "
         << iPos << endl;

    // look for a specific character beginning in the third position
    iPos = str1.find_first_of ('e', 2);

    cout << "'e' found at position " << iPos << endl;

}

Program Output is:

The string to search is 'Heartbeat'
Element in 'abcde' found at position 1
Element in 'abcde' found at position 2
Element in 'aeiou' found at position 6
Element in 'aeiou' found at position 1
'e' found at position 6