C语言 在无符号长数组和uint8_t数组之间进行转换

Question

我正在尝试读取和写入无符号长类型值到NFC卡。

我正在使用pn532模块，MifareUltralight卡和Adafruit库。mifareultralight_WritePage函数似乎只接受 4 字节大小为 uint8_t 类型的数组。

所以我想将一个四字节长类型值一一存储在Uint8_t数组中，并将一个 4 字节长度的Uint8_t数组转换为一个长类型变量。

#include <Adafruit_PN532.h>
...
uint8_t writeBuffer[4] = { 18, 52, 86, 120 };
nfc.mifareultralight_WritePage(8, writeBuffer);

uint8_t readBuffer[4];
success = nfc.mifareultralight_ReadPage(i, &readBuffer[0]);
    if (success) {
        nfc.PrintHex(readBuffer, 4);
}

Answer 1

in

uint8_t writeBuffer[4] = { 18, 52, 86, 120 };

如果索引 0 包含较低的字节，例如

uint8_t writeBuffer[4] = { 18, 52, 86, 120 };
unsigned long v = writeBuffer[0];
for (size_t i = 1; i != 4; ++i)
  v += ((unsigned long) writeBuffer[i]) << (i * 8);

如果索引 0 包含更高的字节，例如

uint8_t writeBuffer[4] = { 18, 52, 86, 120 };
unsigned long v = writeBuffer[3];
for (size_t i = 1; i != 4; ++i)
  v += ((unsigned long) writeBuffer[3 - i]) << (i * 8);