typedef struct{
    int nSize;
    int nMaxCapacity;
    char* szStr;
} StringBuilder;

StringBuilder* Initialize(int nCapacity);
void Append(StringBuilder *strBuilder, char* szStr);
void Clear(StringBuilder *strBuilder);

int _tmain(int argc, _TCHAR* argv[])
{
    StringBuilder* strBuilder = Initialize(1);
    Append(strBuilder, "I'm the string! :)\0");
    printf("%s", strBuilder);
    Clear(strBuilder);

    getchar();

    return 0;
}

StringBuilder* Initialize(int nCapacity)
{
    StringBuilder* strBuilder = (StringBuilder*)malloc(sizeof(StringBuilder));
    strBuilder->nMaxCapacity = nCapacity;
    strBuilder->nSize = 0;
    strBuilder->szStr = (char*)malloc(1);
    strBuilder->szStr = "\0";

    return strBuilder;
}

void Clear(StringBuilder *strBuilder)
{
    if(strBuilder != NULL)
        free(strBuilder);
}

void Append(StringBuilder *strBuilder, char* szStr)
{
    if(strBuilder->nSize + strlen(szStr) > strBuilder->nMaxCapacity)
        if((strBuilder->nMaxCapacity * 2) <= 2147483647)
        {
            strBuilder = (StringBuilder*)realloc(strBuilder, (strBuilder->nMaxCapacity * 2));
            strBuilder->nMaxCapacity = strBuilder->nMaxCapacity * 2;
        }
        else
            return; // overflow
    else
        strBuilder = (StringBuilder*)realloc(strBuilder, strBuilder->nSize + strlen(szStr));

    strBuilder->nSize += strlen(szStr);
    strBuilder->szStr = (char*)realloc(strBuilder->szStr, strBuilder->nSize + 2);

    strcat(strBuilder->szStr, szStr);
}