NSData 转 Int 的几种方法

一、直接使用NSData中的方法getBytes: length: 进行转换

int i;
[data getBytes:&i length:sizeof(i)];

二、最简单的办法

int i =  *(int *)([data bytes]);

三、移位

// {[LSB], ..., ... ,[MSB]}
+ (int) intFromDataReverse:(NSData *)data
{
    int intSize = sizeof(int);// change it to fixe length
    unsigned char * buffer = malloc(intSize * sizeof(unsigned char));
    [data getBytes:buffer length:intSize];
    int num = 0;
    for (int i = intSize - 1; i >= 0; i--) {
        num = (num << 8) + buffer[i];
    }
    free(buffer);
    return num;
}

注意： 如果通过dataFromInt：方法将int数据转换成NSData数据，那么再转换回来，则需要通过方法intFromData：来完成。

+ (NSData *) dataFromInt:(int)num {
    unsigned char * arr = (unsigned char *) malloc(sizeof(num) * sizeof(unsigned char));
    for (int i = sizeof(num) - 1 ; i >= 0; i --) {
        arr[i] = num & 0xFF;
        num = num >> 8;
    }
    NSData * data = [NSData dataWithBytes:arr length:sizeof(num)];
    free(arr);
    return data;
}

// {[MSB], ..., ... ,[LSB]}
+ (int) intFromData:(NSData *)data
{
    int intSize = sizeof(int); // change it to fixe length
    unsigned char * buffer = malloc(intSize * sizeof(unsigned char));
    [data getBytes:buffer length:intSize];
    int num = 0;
    for (int i = 0; i < intSize; i++) {
        num = (num << 8) + buffer[i];
    }
    free(buffer);
    return num;
}