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



typedef struct {
    char* data;
    int length;
    int capacity;
} String;

String NewString(const char* initialData) {
    String str;
    str.length = 0;
    str.capacity = 0;
    str.data = NULL;

    if (initialData != NULL) {
        int initialLength = strlen(initialData);
        str.capacity = initialLength + 1;
        str.data = (char*)malloc(str.capacity * sizeof(char));
        if (str.data != NULL) {
            strcpy(str.data, initialData);
            str.length = initialLength;
        }
    }

    return str;
}

void appendString(String* str, const char* additionalData) {
    if (additionalData != NULL) {
        int additionalLength = strlen(additionalData);

        if (str->length + additionalLength + 1 > str->capacity) {
            int newCapacity = (str->length + additionalLength + 1) * 2;
            char* newData = (char*)realloc(str->data, newCapacity * sizeof(char));
            if (newData != NULL) {
                str->data = newData;
                str->capacity = newCapacity;
            } else {
                // 内存不足，无法追加字符串
                return;
            }
        }

        strcpy(str->data + str->length, additionalData);
        str->length += additionalLength;
    }
}

void printString(const String* str) {
    if (str != NULL && str->data != NULL) {
        printf("%s", str->data);
    }
}

void freeString(String* str) {
    if (str != NULL && str->data != NULL) {
        free(str->data);
        str->data = NULL;
        str->length = 0;
        str->capacity = 0;
    }
}

int main() {
    String myString = NewString("Hello, ");
    appendString(&myString, "world!");

    printString(&myString);

    freeString(&myString);

    return 0;
}