下面是我通过分析数据得到的正式版本iOS主版本号和build版本号的对应关系，记录下方面后续查询。未全量验证是否都正确，请谨慎参考。统计数据截止日期2019.09.20，更新至iOS 13.0。
8.0|12A365
8.0.1|12A402
8.0.2|12A405
8.1|12B411
8.1.1|12B435,12B436
8.1.2|12B440
8.1.3|12B466
8.2|12D508
8.3|12F70
8.4|12H143
8.4.1|12H321
9.0|13A342,13A344
9.0.1|13A404,13A405
9.0.2|13A452
9.1|13B143
9.2|13C75
9.2.1|13D15,13D20
9.3|13E233,13E234
9.3.1|13E238
9.3.2|13F69
9.3.3|13G34
9.3.4|13G35
9.3.5|13G36
10.0|14A346
10.0.1|14A403
10.0.2|14A456
10.0.3|14A551
10.1|14B72,14B72c
10.1.1|14B100,14B150
10.2|14C92
10.2.1|14D10,14D27
10.3|14E277
10.3.1|14E304
10.3.2|14F89
10.3.3|14G60
11.0|15A372
11.0.1|15A402,15A403,15A8391
11.0.2|15A421
11.0.3|15A432
11.1|15B93,15B101
11.1.1|15B150
11.1.2|15B202
11.2|15C114
11.2.1|15C153
11.2.2|15C202
11.2.5|15D60
11.2.6|15D100
11.3|15E216,15E218
11.3.1|15E302
11.4|15F79
11.4.1|15G77
12.0|16A366
12.0.1|16A404,16A405
12.1|16B92,16B94
12.1.1|16C50
12.1.2|16C101,16C104
12.1.3|16D39,16D40
12.1.4|16D57
12.2|16E227
12.3|16F156
12.3.1|16F203
12.3.2|16F250
12.4|16G77
12.4.1|16G102
13.0|17A577
获取iOS系统主版本号
NSString *version = [UIDevice currentDevice].systemVersion;
获取iOS系统内部版本号
int name[2] = {CTL_KERN, KERN_OSVERSION};
u_int nlen = sizeof(name) / sizeof(name[0]);
sysctl(name, nlen, version, &versionlen, NULL, 0);