我总是把它们保存在Constants.h文件中:

#define IS_IPHONE5 (([[UIScreen mainScreen] bounds].size.height-568)?NO:YES) 
#define IS_OS_5_OR_LATER    ([[[UIDevice currentDevice] systemVersion] floatValue] >= 5.0)
#define IS_OS_6_OR_LATER    ([[[UIDevice currentDevice] systemVersion] floatValue] >= 6.0)
#define IS_OS_7_OR_LATER    ([[[UIDevice currentDevice] systemVersion] floatValue] >= 7.0)
#define IS_OS_8_OR_LATER    ([[[UIDevice currentDevice] systemVersion] floatValue] >= 8.0)

一个在obj - c++ 11中更通用的版本(你可能会用NSString/C函数替换其中的一些东西，但这不是那么冗长。这给了你两种机制。splitSystemVersion为你提供了一个包含所有部分的数组，如果你只是想打开主版本(例如switch([self splitSystemVersion][0]) {case 4: break;案例5:断裂;})。

#include <boost/lexical_cast.hpp>

- (std::vector<int>) splitSystemVersion {
    std::string version = [[[UIDevice currentDevice] systemVersion] UTF8String];
    std::vector<int> versions;
    auto i = version.begin();

    while (i != version.end()) {
        auto nextIllegalChar = std::find_if(i, version.end(), [] (char c) -> bool { return !isdigit(c); } );
        std::string versionPart(i, nextIllegalChar);
        i = std::find_if(nextIllegalChar, version.end(), isdigit);

        versions.push_back(boost::lexical_cast<int>(versionPart));
    }

    return versions;
}

/** Losslessly parse system version into a number
 * @return <0>: the version as a number,
 * @return <1>: how many numeric parts went into the composed number. e.g.
 * X.Y.Z = 3.  You need this to know how to compare again <0>
 */
- (std::tuple<int, int>) parseSystemVersion {
    std::string version = [[[UIDevice currentDevice] systemVersion] UTF8String];
    int versionAsNumber = 0;
    int nParts = 0;

    auto i = version.begin();
    while (i != version.end()) {
        auto nextIllegalChar = std::find_if(i, version.end(), [] (char c) -> bool { return !isdigit(c); } );
        std::string versionPart(i, nextIllegalChar);
        i = std::find_if(nextIllegalChar, version.end(), isdigit);

        int part = (boost::lexical_cast<int>(versionPart));
        versionAsNumber = versionAsNumber * 100 + part;
        nParts ++;
    }

    return {versionAsNumber, nParts};
}


/** Assume that the system version will not go beyond X.Y.Z.W format.
 * @return The version string.
 */
- (int) parseSystemVersionAlt {
    std::string version = [[[UIDevice currentDevice] systemVersion] UTF8String];
    int versionAsNumber = 0;
    int nParts = 0;

    auto i = version.begin();
    while (i != version.end() && nParts < 4) {
        auto nextIllegalChar = std::find_if(i, version.end(), [] (char c) -> bool { return !isdigit(c); } );
        std::string versionPart(i, nextIllegalChar);
        i = std::find_if(nextIllegalChar, version.end(), isdigit);

        int part = (boost::lexical_cast<int>(versionPart));
        versionAsNumber = versionAsNumber * 100 + part;
        nParts ++;
    }

    // don't forget to pad as systemVersion may have less parts (i.e. X.Y).
    for (; nParts < 4; nParts++) {
        versionAsNumber *= 100;
    }

    return versionAsNumber;
}

float deviceOSVersion = [[[UIDevice currentDevice] systemVersion] floatValue];
float versionToBeCompared = 3.1.3; //(For Example in your case)

if(deviceOSVersion < versionToBeCompared)
   //Do whatever you need to do. Device version is lesser than 3.1.3(in your case)
else 
   //Device version should be either equal to the version you specified or above

+(BOOL)doesSystemVersionMeetRequirement:(NSString *)minRequirement{

// eg  NSString *reqSysVer = @"4.0";


  NSString *currSysVer = [[UIDevice currentDevice] systemVersion];

  if ([currSysVer compare:minRequirement options:NSNumericSearch] != NSOrderedAscending)
  {
    return YES;
  }else{
    return NO;
  }


}

if (floor(NSFoundationVersionNumber) > NSFoundationVersionNumber_iOS_6_1) {
        // Your code here
}

当然，其中NSFoundationVersionNumber_iOS_6_1必须更改为by适用于您要检查的iOS版本。我现在所写的内容在测试设备是否运行iOS7或之前的版本时可能会经常用到。

使用nv-ios-version项目(Apache License, Version 2.0)中包含的Version类，很容易获取和比较iOS版本。下面的示例代码转储iOS版本，并检查版本是否大于或等于6.0。

// Get the system version of iOS at runtime.
NSString *versionString = [[UIDevice currentDevice] systemVersion];

// Convert the version string to a Version instance.
Version *version = [Version versionWithString:versionString];

// Dump the major, minor and micro version numbers.
NSLog(@"version = [%d, %d, %d]",
    version.major, version.minor, version.micro);

// Check whether the version is greater than or equal to 6.0.
if ([version isGreaterThanOrEqualToMajor:6 minor:0])
{
    // The iOS version is greater than or equal to 6.0.
}

// Another way to check whether iOS version is
// greater than or equal to 6.0.
if (6 <= version.major)
{
    // The iOS version is greater than or equal to 6.0.
}

项目页面:nv-ios-version TakahikoKawasaki / nv-ios-version

博客:获取并比较iOS版本在运行时与版本类 获取并比较iOS版本在运行时与版本类