C 设置位后打印变量

我试图在8位变量中设置一位。 每次我在设置一个特定位后打印变量时，我总是得到值1

uint8 value;
value = (1<<1 || value)
printf(%x \n,value); //prints 1 instead of 2
value = (1<<2 || value)
printf(%x \n,value); //prints 1 instead of 4

您正在使用布尔“或”| |。按位“或”是|

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另外，您还没有初始化值，所以不能期望它是任何值。

不，您不会这样做

要设置一个位，请使用1

例如，要设置最低有效位，请使用1或

即：

要设置位1：

 unsigned char val = 4;
 // set bit 1
 val |= 1 << 1;
 printf("Value now: %x\n", val);

一个完整的例子

#include <stdio.h>

char* get_binary(unsigned char buffer, char* binary) {
    for (int i = 0; i < 8; ++i) {
        int bit = (buffer >> i) & 1;
        binary[7 - i] = bit ? '1' : '0';
    }
    return binary;
}


int main() {

    unsigned char val = 4;  // val now 100
    int bits_to_shift;
    unsigned char buffer[10] = { 0 };
    unsigned char* p = buffer;
    // set bit 0
    val |= 1;  
    printf("Value now: %x, binary=%s\n", val, get_binary(val, p));  // val now 5 :- 101

    // To set bit 1 (ie set so we have 111), shift to position then OR

    // set bit 1
    bits_to_shift = 1;
    val |= 1 << bits_to_shift;
    printf("Value now: %x, binary=%s\n", val, get_binary(val, p));  // val now 7 :- 111 

    // set bit 3
    bits_to_shift = 3;
    val |= 1 << bits_to_shift;
    printf("Value now: %x, binary=%s\n", val, get_binary(val, p));  // val now F :- 1111
}

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您需要按位OR，而不是逻辑OR:| not | | |，因为| |被视为布尔值。任何_but _zero或任何_but _zero都是TRUE，TRUE是1。@user996142按位OR和逻辑OR都执行布尔或运算。。。不同之处在于它们对|单个位位置| |整个值执行的操作值也未初始化。@Dmitri:FYI，该标准区分按位和逻辑布尔运算符。

#include <stdio.h>

char* get_binary(unsigned char buffer, char* binary) {
    for (int i = 0; i < 8; ++i) {
        int bit = (buffer >> i) & 1;
        binary[7 - i] = bit ? '1' : '0';
    }
    return binary;
}


int main() {

    unsigned char val = 4;  // val now 100
    int bits_to_shift;
    unsigned char buffer[10] = { 0 };
    unsigned char* p = buffer;
    // set bit 0
    val |= 1;  
    printf("Value now: %x, binary=%s\n", val, get_binary(val, p));  // val now 5 :- 101

    // To set bit 1 (ie set so we have 111), shift to position then OR

    // set bit 1
    bits_to_shift = 1;
    val |= 1 << bits_to_shift;
    printf("Value now: %x, binary=%s\n", val, get_binary(val, p));  // val now 7 :- 111 

    // set bit 3
    bits_to_shift = 3;
    val |= 1 << bits_to_shift;
    printf("Value now: %x, binary=%s\n", val, get_binary(val, p));  // val now F :- 1111
}