Question

我有一个小的未排序数组，我想找到特定值的索引。 C ++是否具有内置的顺序搜索功能，或者您是否每次都自己编写循环？

我特意使用C风格的数组，如：

std::string arr[5] = { "EVEN", "ODD", "NONE", "MARK", "SPACE" };

我需要用户提供的值的索引。

Answer 1

使用STL- 算法 -library中的std::find()或特定容器的find() - 方法。

Answer 2

std::find()应该有效：

#include <stdio.h>
#include <algorithm>
#include <string>

using std::string;

std::string arr[5] = { "EVEN", "ODD", "NONE", "MARK", "SPACE" };


int main() {

    string* pArrEnd = arr + sizeof( arr)/sizeof(arr[0]);

    string* pFound = std::find( arr, pArrEnd, "MARK");

    if (pFound == pArrEnd) {
        printf( "not found\n");
    }
    else {
        printf( "%s was found at index %d\n", pFound->c_str(), pFound - arr);
        printf( "or using STL: %d\n", std::distance( arr, pFound));
    }

    return 0;
}

Answer 3

您可以在STL容器以外的容器上使用STL算法。例如，你可以在C风格的数组中使用std :: find（）：

// alloc the array
static const size_t numItems = 100000;
int * items = new int[numItems];

// fill the array
for( size_t n = 0; n < numItems; ++n )
    items[n] = n;

// find 42 using std::find()
int* found = std::find(&items[0], &items[numItems], 42);
if( found == &items[numItems] )
{
    // this is one past the end, so 42 was not found
    items[0] = 42;
}
else
{
    // we found the first instance of 42 at this location
    // change it to 43
    *found = 43;
}

Answer 4

我想你需要索引而不是迭代器。

int main()
{
    // for c++ vector
    typedef int Element;
    typedef std::vector<Element> CppVector;

    CppVector v;
    v.push_back( 2 );
    v.push_back( 4 );
    v.push_back( 8 );
    v.push_back( 6 );

    const Element el = 4;

    CppVector::const_iterator it = std::find( v.begin(), v.end(), el );
    if ( it == v.end() )
    {
        std::cout << "there is no such element" << std::endl;
    }
    else
    {
        const CppVector::size_type index = it - v.begin();
        std::cout << "index = " << index << std::endl;
    }

    // for C array
    typedef Element CVector[4];
    CVector cv;
    cv[0] = 2;
    cv[1] = 4;
    cv[2] = 8;
    cv[3] = 6;

    const std::size_t cvSize = sizeof( cv ) / sizeof( Element );

    std::cout << "c vector size = " << cvSize << std::endl;

    const Element* cit = std::find( cv, cv + cvSize, el );
    const std::size_t index = cit - cv;

    if ( index >= cvSize )
        std::cout << "there is no such element" << std::endl;
    else
        std::cout << "index = " << index << std::endl;
}

Answer 5

除了已经提到的STL可能性（std::find）之外，还有POSIX函数lsearch（带有c语义）。

C ++是否具有顺序搜索功能？

5 个答案: