Question

我想创建一个模板类的对象＆＃34; stack＆＃34;使用如下所示的if条件并在if条件之外使用它。

template <class TYPE>

class stack{
..
..
};
main()
{
int opt;
cin>>opt;

这是if条件

if(opt == 1)
    stack<int> s;
else
    stack<float> s;

s.push(1);
}

我面临的问题是对象＆＃34; s＆＃34;正在块范围内创建，如果条件，我无法访问该对象。

Answer 1

这很简单。只需将公共代码放在函数模板中即可。

template< class Number >
void foo()
{
    stack<Number> s;
    s.push( 1 );
}

auto main() -> int
{
    int opt;
    cin>>opt;
    opt == 1? foo<int>() : foo<double>();
}

Answer 2

require_once "...filename with get_session_user_id() function...";的类型必须在运行时之前知道，但您可以使用这样的接口：

Answer 3

最后，我找到了答案。以＆＃34;纯虚拟＆＃34;制作功能。在基类。在派生类中定义纯虚函数。在main（）中声明基类型指针* s，然后在if条件下package patriciaTrie; import java.util.ArrayList; import java.util.Scanner; public class Patricia { private TrieNode nodeRoot; private TrieNode nodeFirst; // create a new node public Patricia() { nodeRoot = null; } // inserts a string into the trie public void insert(String s) { if (nodeRoot == null) { nodeRoot = new TrieNode(); nodeFirst = new TrieNode(s); nodeFirst.isWord = true; nodeRoot.next.add(nodeFirst); } else { // nodeRoot.isWrod = false; insert(nodeRoot, s); } } private String checkEdgeString(ArrayList<TrieNode> history, String s) { StringBuilder sb = new StringBuilder(); for (TrieNode nextNodeEdge : history) { int len1 = nextNodeEdge.edge.length(); int len2 = s.length(); int len = Math.min(len1, len2); for (int index = 0; index < len; index++) { if (s.charAt(index) != nextNodeEdge.edge.charAt(index)) { break; } else { char c = s.charAt(index); sb.append(c); } } } return sb.toString(); } private void insert(TrieNode node, String s) { ArrayList<TrieNode> history = new ArrayList<TrieNode>(); for (TrieNode nextNodeEdge : node.getNext()) { history.add(nextNodeEdge); } String communsubString = checkEdgeString(history, s); System.out.println("commun String: " + communsubString); if (!communsubString.isEmpty()) { for (TrieNode nextNode : node.getNext()) { if (nextNode.edge.startsWith(communsubString)) { String substringSplit1 = nextNode.edge .substring(communsubString.length()); String substringSplit2 = s.substring(communsubString .length()); if (substringSplit1.isEmpty() && !substringSplit2.isEmpty()) { // 1. case: aba, abaxyz } else if (substringSplit2.isEmpty() && !substringSplit1.isEmpty()) { // 2. case: abaxyz, aba ArrayList<TrieNode> cacheNextNode = new ArrayList<TrieNode>(); System.out.println("node edge string is longer."); if (nextNode.getNext() != null && !nextNode.getNext().isEmpty()) { for (TrieNode subword : nextNode.getNext()) { subword.edge = substringSplit1.concat(subword.edge); //This line cacheNextNode.add(subword); } nextNode.getNext().clear(); nextNode.edge = communsubString; nextNode.isWord = true; TrieNode child = new TrieNode(substringSplit1); child.isWord = true; nextNode.next.add(child); for(TrieNode node1 : cacheNextNode){ child.next.add(node1); System.out.println("Test one"); } cacheNextNode.clear(); }else{ nextNode.edge = communsubString; TrieNode child = new TrieNode(substringSplit1); child.isWord = true; nextNode.next.add(child); System.out.println("TEST"); } } else if(substringSplit1.isEmpty() && substringSplit2.isEmpty()){ //3. case: aba and aba. nextNode.isWord = true; }else { // 4. Case: abauwt and abaxyz //if(nextNode.getNext().isEmpty()) } break; } } } else { // There is no commun substring. System.out.println("There is no commun substring"); TrieNode child = new TrieNode(s); child.isWord = true; node.next.add(child); } } public static void main(String[] args) { Patricia p = new Patricia(); Scanner s = new Scanner(System.in); while (s.hasNext()) { String op = s.next(); if (op.equals("INSERT")) { p.insert(s.next()); } } } class TrieNode { ArrayList<TrieNode> next = new ArrayList<TrieNode>(); String edge; boolean isWord; // To create normal node. TrieNode(String edge) { this.edge = edge; } // To create the root node. TrieNode() { this.edge = ""; } public ArrayList<TrieNode> getNext() { return next; } public String getEdge() { return edge; } } }或s = new stackDerived<int>。

s = new stackDerived<char>

在C ++中使用if条件仅声明一个变量（模板）

3 个答案: