将一些字节从无符号char转换为int

Question

I want to convert some bytes to an int. This is my code so far:

unsigned char *bytePtr = (unsigned char *)[aNSDataFrame];

I want to take 4 bytes from this unsigned char: myFrame[10] , myFrame[11] , myFrame[12] and myFrame[13] and convert them to an integer.

Answer 1

int bytesToInt(unsigned char* b, unsigned length)
{

    int val = 0;

    int j = 0;

    for (int i = length-1; i >= 0; --i)
    {
        val += (b[i] & 0xFF) << (8*j);
        ++j;
    }
    return val;
}

Answer 2

you can do,

int a;
a=myframe[10];
a=a<<8;
a=a|myframe[11];
a=a<<8;
a=a|myframe[12];
a=a<<8;
a=a|myframe[13];

this will create integer containing those bytes

Answer 3

int val = *(const int*)&myFrame[10];