qt 实现Cstring.IsEmpty()==FALSE一样的功能

可以使用QString类的isEmpty()函数来实现类似的功能，例如：

QString str = "hello";
if (!str.isEmpty()) {
// do something
}

这里的!str.isEmpty()相当于Cstring.IsEmpty()==FALSE。

相关问题

qt 实现FILE* myfp=open(Cstring,"a+")一样的功能

可以使用Qt的QFile类来实现类似的功能，具体代码如下：

QFile file(QString::fromStdString(Cstring));
if (file.open(QIODevice::WriteOnly | QIODevice::Append)) {
QTextStream out(&file);
out << "Hello, world!" << endl;
file.close();
}

这段代码会打开一个文件，如果文件不存在则会创建一个新文件，然后将文本写入文件末尾。

#include<cstring> #include<iostream> using namespace std; typedef struct { int weight; int parent,lchild,rchild; }HTNode,*HuffmanTree; typedef char **HuffmanCode; void Select(HuffmanTree HT,int len,int &s1,int &s2) { int i,min1=32767,min2=32767; for(i=1;i<=len;i++) { if(HT[i].weight<min1&&HT[i].parent==0) { s2=s1; min2=min1; min1=HT[i].weight; s1=i; } else if(HT[i].weight<min2&&HT[i].parent==0) { min2=HT[i].weight; s2=i; } } } void CreatHuffmanTree(HuffmanTree &HT,int n) { int m,s1,s2,i; if(n<=1) return; m=2*n-1; HT=new HTNode[m+1]; for(i=1;i<=m;++i) { HT[i].parent=0; HT[i].lchild=0; HT[i].rchild=0; } for(i=1;i<=n;++i) cin >> HT[i].weight; for(i=n+1;i<=m;++i) { ; HT[s1].parent= ; HT[s2].parent= ; HT[i].lchild= ; HT[i].rchild= ; HT[i].weight= ; } } void print(HuffmanTree HT,int n) { for(int i=1;i<=2*n-1;i++) cout << HT[i].weight << " " << HT[i].parent << " " << HT[i].lchild << " " << HT[i].rchild << endl; } int main() { HuffmanTree HT; int n; cin >> n; CreatHuffmanTree(HT,n); print(HT,n); return 0; }填完这段代码

这段代码是一个创建哈夫曼树的函数，需要填写一些缺少的代码段。

在函数中，需要调用 `Select` 函数来选择权值最小的两个节点，并将它们合并成一个新的节点。在合并的过程中，需要给新节点的 `parent`、`lchild`、`rchild`、`weight` 成员变量赋值。

下面是填好代码的函数：

#include <cstring>
#include <iostream>
using namespace std;

typedef struct {
    int weight;
    int parent, lchild, rchild;
} HTNode, *HuffmanTree;

typedef char **HuffmanCode;

void Select(HuffmanTree HT, int len, int &s1, int &s2) {
    int i, min1 = 32767, min2 = 32767;
    for (i = 1; i <= len; i++) {
        if (HT[i].weight < min1 && HT[i].parent == 0) {
            s2 = s1;
            min2 = min1;
            min1 = HT[i].weight;
            s1 = i;
        } else if (HT[i].weight < min2 && HT[i].parent == 0) {
            min2 = HT[i].weight;
            s2 = i;
        }
    }
}

void CreatHuffmanTree(HuffmanTree &HT, int n) {
    int m, s1, s2, i;
    if (n <= 1)
        return;
    m = 2 * n - 1;
    HT = new HTNode[m + 1];
    for (i = 1; i <= m; ++i) {
        HT[i].parent = 0;
        HT[i].lchild = 0;
        HT[i].rchild = 0;
    }
    for (i = 1; i <= n; ++i)
        cin >> HT[i].weight;
    for (i = n + 1; i <= m; ++i) {
        Select(HT, i - 1, s1, s2);
        HT[s1].parent = i;
        HT[s2].parent = i;
        HT[i].lchild = s1;
        HT[i].rchild = s2;
        HT[i].weight = HT[s1].weight + HT[s2].weight;
    }
}

void print(HuffmanTree HT, int n) {
    for (int i = 1; i <= 2 * n - 1; i++)
        cout << HT[i].weight << " " << HT[i].parent << " " << HT[i].lchild << " " << HT[i].rchild << endl;
}

int main() {
    HuffmanTree HT;
    int n;
    cin >> n;
    CreatHuffmanTree(HT, n);
    print(HT, n);
    return 0;
}