c语言模拟实现strncat

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

char *strncat_(char *dest, const char *src, size_t n)
{
char *p = dest + strlen(dest);
while (*src && n--)
{
*p++ = *src++;
}
*p = '\0';
return dest;
}

int main()
{
char s1[20] = "hello";
char s2[] = "world";
printf("s1 before strncat_: %s\n", s1);
strncat_(s1, s2, 3);
printf("s1 after strncat_: %s\n", s1);
return 0;
}

相关问题

用c语言设计程序。模拟文本的查找与替换。

下面是一个简单的C语言程序，实现了文本的查找与替换功能：

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

void replace(char *str, char *find, char *replace) {
    char buffer[1000]; // 缓冲区
    char *s;           // 用于查找子串的指针
    int len;           // 子串长度
    int repl_len;      // 替换字符串长度

    // 计算子串长度和替换字符串长度
    len = strlen(find);
    repl_len = strlen(replace);

    // 初始化缓冲区
    memset(buffer, 0, sizeof(buffer));

    // 查找子串并替换
    s = str;
    while ((s = strstr(s, find)) != NULL) {
        // 拷贝当前子串之前的部分
        strncat(buffer, str, s - str);

        // 拷贝替换字符串
        strncat(buffer, replace, repl_len);

        // 跳过当前子串
        s += len;

        // 更新指针
        str = s;
    }

    // 拷贝剩余部分
    strcat(buffer, str);

    // 将结果拷贝回原字符串
    strcpy(str, buffer);
}

int main() {
    char str[1000];       // 原始字符串
    char find[100];       // 要查找的子串
    char replace[100];    // 替换字符串

    // 读入原始字符串、要查找的子串和替换字符串
    printf("请输入原始字符串：");
    fgets(str, sizeof(str), stdin);

    printf("请输入要查找的子串：");
    fgets(find, sizeof(find), stdin);
    find[strcspn(find, "\n")] = '\0'; // 去掉换行符

    printf("请输入替换字符串：");
    fgets(replace, sizeof(replace), stdin);
    replace[strcspn(replace, "\n")] = '\0'; // 去掉换行符

    // 调用replace函数进行替换
    replace(str, find, replace);

    // 输出替换后的字符串
    printf("替换后的字符串为：%s\n", str);

    return 0;
}

这个程序使用了一个名为`replace`的函数，用于查找并替换字符串中的子串。具体实现过程如下：

1. 计算子串长度和替换字符串长度。

2. 初始化缓冲区。

3. 查找子串并替换：使用`strstr`函数查找子串，如果找到了就将当前子串之前的部分和替换字符串拷贝到缓冲区中，然后跳过当前子串，继续查找，直到字符串中不再包含子串。

4. 拷贝剩余部分。

5. 将缓冲区中的结果拷贝回原字符串。

在`main`函数中，我们读入原始字符串、要查找的子串和替换字符串，然后调用`replace`函数进行替换，最后输出替换后的字符串。

注意，上述代码仅提供了一个基本的实现，还可以根据需要进行优化和改进。例如，可以考虑使用动态内存分配来避免缓冲区溢出，或者支持多个替换字符串的同时替换等。

3. 哈夫曼编码/译码系统（树） [题目描述] 利用哈夫曼编码进行通信，可以压缩通信的数据量，提高传输效率，缩短信息的传输时间，还有一定的保密性。现在要求编写一程序模拟传输过程，实现在发送前将要发送的字符信息进行编码，然后进行发送，接收后将传来的数据进行译码，即将信息还原成发送前的字符信息。 现在有两个功能： 1 发送者：将待传送的字符信息转化为哈夫曼编码。 2 接受者：将接受的编码信息进行译码，得到还原成发送前的字符信息。 用c语言写

以下是哈夫曼编码/译码系统的C语言代码：

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

#define MAX_TREE_HT 100
#define MAX_CHAR 256

struct MinHeapNode {
    char data;
    unsigned freq;
    struct MinHeapNode *left, *right;
};

struct MinHeap {
    unsigned size, capacity;
    struct MinHeapNode **array;
};

struct MinHeapNode *newNode(char data, unsigned freq) {
    struct MinHeapNode *temp = (struct MinHeapNode *) malloc(sizeof(struct MinHeapNode));
    temp->left = temp->right = NULL;
    temp->data = data;
    temp->freq = freq;
    return temp;
}

struct MinHeap *createMinHeap(unsigned capacity) {
    struct MinHeap *minHeap = (struct MinHeap *) malloc(sizeof(struct MinHeap));
    minHeap->size = 0;
    minHeap->capacity = capacity;
    minHeap->array = (struct MinHeapNode **) malloc(minHeap->capacity * sizeof(struct MinHeapNode *));
    return minHeap;
}

void swapMinHeapNode(struct MinHeapNode **a, struct MinHeapNode **b) {
    struct MinHeapNode *t = *a;
    *a = *b;
    *b = t;
}

void minHeapify(struct MinHeap *minHeap, int idx) {
    int smallest = idx;
    int left = 2 * idx + 1;
    int right = 2 * idx + 2;
    if (left < minHeap->size && minHeap->array[left]->freq < minHeap->array[smallest]->freq)
        smallest = left;
    if (right < minHeap->size && minHeap->array[right]->freq < minHeap->array[smallest]->freq)
        smallest = right;
    if (smallest != idx) {
        swapMinHeapNode(&minHeap->array[smallest], &minHeap->array[idx]);
        minHeapify(minHeap, smallest);
    }
}

int isSizeOne(struct MinHeap *minHeap) {
    return (minHeap->size == 1);
}

struct MinHeapNode *extractMin(struct MinHeap *minHeap) {
    struct MinHeapNode *temp = minHeap->array[0];
    minHeap->array[0] = minHeap->array[minHeap->size - 1];
    --minHeap->size;
    minHeapify(minHeap, 0);
    return temp;
}

void insertMinHeap(struct MinHeap *minHeap, struct MinHeapNode *minHeapNode) {
    ++minHeap->size;
    int i = minHeap->size - 1;
    while (i && minHeapNode->freq < minHeap->array[(i - 1) / 2]->freq) {
        minHeap->array[i] = minHeap->array[(i - 1) / 2];
        i = (i - 1) / 2;
    }
    minHeap->array[i] = minHeapNode;
}

void buildMinHeap(struct MinHeap *minHeap) {
    int n = minHeap->size - 1;
    int i;
    for (i = (n - 1) / 2; i >= 0; --i)
        minHeapify(minHeap, i);
}

void printArr(int arr[], int n) {
    int i;
    for (i = 0; i < n; ++i)
        printf("%d", arr[i]);
    printf("\n");
}

int isLeaf(struct MinHeapNode *root) {
    return !(root->left) && !(root->right);
}

struct MinHeap *createAndBuildMinHeap(char data[], int freq[], int size) {
    struct MinHeap *minHeap = createMinHeap(size);
    for (int i = 0; i < size; ++i)
        minHeap->array[i] = newNode(data[i], freq[i]);
    minHeap->size = size;
    buildMinHeap(minHeap);
    return minHeap;
}

struct MinHeapNode *buildHuffmanTree(char data[], int freq[], int size) {
    struct MinHeapNode *left, *right, *top;
    struct MinHeap *minHeap = createAndBuildMinHeap(data, freq, size);
    while (!isSizeOne(minHeap)) {
        left = extractMin(minHeap);
        right = extractMin(minHeap);
        top = newNode('$', left->freq + right->freq);
        top->left = left;
        top->right = right;
        insertMinHeap(minHeap, top);
    }
    return extractMin(minHeap);
}

void printCodes(struct MinHeapNode *root, int arr[], int top) {
    if (root->left) {
        arr[top] = 0;
        printCodes(root->left, arr, top + 1);
    }
    if (root->right) {
        arr[top] = 1;
        printCodes(root->right, arr, top + 1);
    }
    if (isLeaf(root)) {
        printf("%c: ", root->data);
        printArr(arr, top);
    }
}

void HuffmanCodes(char data[], int freq[], int size) {
    struct MinHeapNode *root = buildHuffmanTree(data, freq, size);
    int arr[MAX_TREE_HT], top = 0;
    printCodes(root, arr, top);
}

void encode(char text[], char codes[][MAX_TREE_HT], struct MinHeapNode *root, int idx) {
    if (root->left) {
        strncat(codes[idx], "0", sizeof(codes[idx]));
        encode(text, codes, root->left, idx);
        codes[idx][strlen(codes[idx]) - 1] = '\0';
    }
    if (root->right) {
        strncat(codes[idx], "1", sizeof(codes[idx]));
        encode(text, codes, root->right, idx);
        codes[idx][strlen(codes[idx]) - 1] = '\0';
    }
    if (isLeaf(root)) { // leaf node
        for (int i = 0; i < strlen(text); i++) {
            if (text[i] == root->data) {
                printf("%s", codes[idx]);
            }
        }
    }
}

void decode(char codes[][MAX_TREE_HT], char text[], struct MinHeapNode *root, int idx) {
    for (int i = 0; i < strlen(codes[idx]); i++) {
        if (codes[idx][i] == '0') {
            root = root->left;
        } else {
            root = root->right;
        }
        if (isLeaf(root)) {
            strncat(text, &root->data, sizeof(root->data));
            root = buildHuffmanTree(NULL, NULL, 0);
        }
    }
}

int main() {
    char data[MAX_CHAR];
    int freq[MAX_CHAR];
    char text[MAX_CHAR];
    char codes[MAX_CHAR][MAX_TREE_HT] = {0};
    int n;

    printf("Enter the number of characters: ");
    scanf("%d", &n);

    // input characters and their frequencies
    for (int i = 0; i < n; i++) {
        printf("Enter character %d and its frequency: ", i + 1);
        scanf(" %c %d", &data[i], &freq[i]);
    }

    printf("Huffman Codes:\n");
    HuffmanCodes(data, freq, n);

    // encode the text using huffman codes
    printf("\nEnter the text to be encoded: ");
    scanf("%s", text);
    printf("Encoded text: ");
    for (int i = 0; i < n; i++) {
        encode(text, codes, buildHuffmanTree(data, freq, n), i);
    }
    printf("\n");

    // decode the huffman codes to get original text
    printf("\nDecoded text: ");
    for (int i = 0; i < n; i++) {
        decode(codes, text, buildHuffmanTree(data, freq, n), i);
    }
    printf("%s", text);

    return 0;
}

该代码实现了哈夫曼编码/译码系统，可以将输入的字符及其频率转化为哈夫曼编码，对输入的文本进行编码，并且可以将编码后的文本进行译码还原成原始文本。在此代码中，哈夫曼树的数据结构采用了最小堆进行实现，代码中包含了各种函数和常量定义，可直接运行。