Question

我正在研究一种C ++代码，它将值连接成一个用于I2C消息系统的字符串。我正确地解决了消息传递问题，但是当我将字符串连接在一起时，代码错误地将我想要的三个值连接到字符串上。我写的代码如下：

void concatint(int value1, char address1, char address2)
{
    int alive1 = static_cast<int>(address1);
    int alive2 = static_cast<int>(address2);
    char* alive3 = (char*)malloc(sizeof(address1));
    char* alive4 = (char*)malloc(sizeof(address2));
    //alive3 = address1;
    //alive4 = address2;
    sprintf(alive3, "%2d", address1);
    sprintf(alive4, "%2d", address2);
    if (value1 < 10)
        readlength = 1;
    if (value1 >= 10 && value1 < 100)
        readlength = 2;
    if (value1 >= 100 && value1 < 1000)
        readlength = 3;
    if (value1 >= 1000 && value1 < 10000)
        readlength = 4;
    if (value1 >= 10000 && value1 < 100000)
        readlength = 5;
    if (value1 >= 100000 && value1 < 1000000)
        readlength = 6;
    if (value1 >= 1000000 && value1 < 10000000)
        readlength = 7;
    if (value1 >= 10000000 && value1 < 100000000)
        readlength = 8;
    *writedata = 0;
    itoa(value1, writedata, 10);
    strcpy(writeaddress, &address1);
    strcat(writeaddress, &address2);
    strcat(writeaddress, writedata);
    strcpy(readaddress, address1);
    strcat(readaddress, address2);
    typevalue = 1;
}

此功能的输入为：

concatint(5, ' ', ' ');

其中两个地址值是两个ASCii字符。

此代码的结果应为：''''5，ASCii字符在值之前连接。但是，当我运行代码时，我得到的结果是：

" \005  \0055"

我的代码似乎在我的角色之间连接了一个额外的角色，我不确定我上面的代码在哪里添加。我已经完成了代码，一切都应该正常，不确定我的问题在哪里。

Answer 1

前八行有未定义的行为：

void concatint(int value1, char address1, char address2)
{
    int alive1 = static_cast<int>(address1);
    int alive2 = static_cast<int>(address2);
    // Note that address1 is a char, not a char*, and as such sizeof(address1)
    // is guaranteed to be 1.  Thus we allocate one byte of storage.
    char * alive3 = (char*) malloc(sizeof(address1));
    char * alive4 = (char*) malloc(sizeof(address2));
    // Here we write two digits and a terminating NUL to that one byte
    // => undefined behaviour.  Cannot reason further about the program.
    sprintf(alive3, "%2d", address1);
    sprintf(alive4, "%2d", address2);

此外：

    strcpy(writeaddress, &address1);

也不起作用。 address1是一个字符。 &address1是指向此字符的指针，但后面没有跟踪NUL字符，因此它也不是传递给strcpy的有效指针。

使用std::string

字符串连接期间添加的额外字符

1 个答案: