c - Converting bytes array to integer -


i have 4-byte array (data) of type uint8_t, represents speed data integer. i'm trying cast array uint32_t integer (speed), multiply speed 10 , restore 4-byte array (data). data format clear in code below. error:

"assignment expression array type"

the code:

volatile uint8_t data[4] = {0x00 , 0x00, 0x00, 0x00}; volatile uint32_t speed; speed=( uint32_t)*data; speed=speed*10; data=(uint8_t*)speed;

your code doesn't work because during data=(uint8_t*)speed; don't "lvalue" data, array type can't used in assignment or form of arithmetic. similarly, speed=( uint32_t)*data; bug because gives first item in array.

the correct way should this:

volatile uint8_t data[4] = {0x00 , 0x00, 0x00, 0x00}; volatile uint32_t speed;  speed = (uint32_t)data[0] << 24 |         (uint32_t)data[1] << 16 |         (uint32_t)data[2] <<  8 |         (uint32_t)data[3] <<  0;  speed=speed*10;  data[0] = (uint8_t) ((speed >> 24) & 0xffu); data[1] = (uint8_t) ((speed >> 16) & 0xffu); data[2] = (uint8_t) ((speed >>  8) & 0xffu); data[3] = (uint8_t) ((speed >>  0) & 0xffu);

this 100% portable , well-defined code. no implicit promotions take place. code not rely on endianess or other implementation-defined behavior. why write code does, when can write code doesn't?


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