uint32_t 类型的 C++ 相等性不比较

Question

我正在读取 RFID 卡并尝试比较 ID，因为一旦卡通过 reader，reader 实际上不止一次读取它，所以我需要丢弃重复项。

更新：以下代码获取卡片 ID

uint32_t IndentifyTag(Adafruit_PN532 rfidReader)
{
    uint8_t tagID[] = { 0, 0, 0, 0, 0, 0, 0 };  // Buffer to store the returned UID
    uint8_t tagIDLength; // Length of the UID (4 or 7 bytes depending on ISO14443A card type)
    uint32_t cardid = tagID[0];
    boolean success = rfidReader.readPassiveTargetID(PN532_MIFARE_ISO14443A, &tagID[0], &tagIDLength);
    if (success) {
        // Display some basic information about the card for testing
        Serial.println("Found an ISO14443A card");
        Serial.print("  UID Length: "); Serial.print(tagIDLength, DEC);     Serial.println(" bytes");
        Serial.print("  UID Value: "); rfidReader.PrintHex(tagID, tagIDLength);

        if (tagIDLength == 4)
        {
            // Mifare Classic card 
            cardid <<= 8;
            cardid |= tagID[1];
            cardid <<= 8;
            cardid |= tagID[2];
            cardid <<= 8;
            cardid |= tagID[3];
            Serial.print("Mifare Classic card #");
            Serial.println(cardid);
        }
        Serial.println("");
    }
    return cardid;
}

在 switch 语句的情况下，我正在测试标签的相等性，如下所示：

uint32_t priorTag = 0000000;
tag = IndentifyTag(entryRFIDReader);

if (tag == priorTag)
{               
    Serial.println("These tags are the same!!!");
}
if (tag != priorTag)
{
    Serial.println("I got here!");
    tagCount += 1;
}
priorTag = tag;
SSerial.println("tagCount = "); Serial.println(tagCount);

问题是，即使 reader 一次读取同一张卡片 3 次或 4 次，它们也永远不会相等，因此 tagCounter 正在计算重复次数。 tag 和 priorTag 都是 uint32_t 类型，因此应该可以与 == 进行比较，但它在这种情况下不起作用。

Found an ISO14443A card
UID Length: 4 bytes
UID Value: 0x92 0x77 0x88 0xBB
Mifare Classic card #7833787

I got here!
tagCount = 1
Found an ISO14443A card
UID Length: 4 bytes
UID Value: 0x92 0x77 0x88 0xBB
Mifare Classic card #7833787

I got here!
tagCount = 2
Found an ISO14443A card
Mifare Classic card #7833787

I got here!
tagCount = 3
Found an ISO14443A card
Mifare Classic card #7833787

I got here!
tagCount = 4

Answer 1

priorTag = tag;
Serial.println("******************************");
Serial.print("Prior tag: "); Serial.println(priorTag);
Serial.print("Current tag: "); Serial.println(tag);

你能解释一下当这四行代码被执行时，你怎么可能在这里看到两个不同的值吗？

Answer 2

变量 priorTag 被声明为过于局部，在您的循环内。因此它在每次迭代开始时始终具有值 0。

将变量 priorTag 的声明移到循环外。

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