时间损耗
time(&temp)返回从CUT（Coordinated Universal Time）时间1970年1月1日00:00:00（称为UNIX系统的Epoch时间）到当前时刻的秒数
clock()返回从“开启这个程序进程”到“程序中调用clock()函数”时之间的CPU时钟计时单元（clock tick）数； 比如，sleep(5)并不占用cpu资源，导致即使sleep了5秒，最后通过clock()来计算时间损耗，仍然不会将这5秒算入损耗之中。
CFAbsoluteTimeGetCurrent() 返回的时钟时间将与会网络时间同步，
mach_absolute_time()和 CACurrentMediaTime()是基于内建时钟的，能够更精确更原子化地测量，并且不会因为外部时间变化而变化（例如时区变化、夏时制、秒突变等）,但它和系统的uptime有关,系统重启后CACurrentMediaTime()会被重置。(比如电脑开机，手机开机到调用函数)
CFTimeInterval GetCFAbsoluteTimeWithBlock(dispatch_block_t block) {
CFAbsoluteTime currentCFTime = CFAbsoluteTimeGetCurrent();
block();
CFAbsoluteTime lastCFTime = CFAbsoluteTimeGetCurrent();
return lastCFTime - currentCFTime;
}
CFTimeInterval GetCACurrentMediaTimeWithBlock(dispatch_block_t block) {
CFTimeInterval currentCATime = CACurrentMediaTime();
block();
CFTimeInterval lastCATime = CACurrentMediaTime();
return lastCATime - currentCATime;
}
CFTimeInterval GetUint64WithBlock(dispatch_block_t block) {
uint64_t currentTime = mach_absolute_time();
block();
uint64_t lastTime = mach_absolute_time();
return (1e-9*(lastTime - currentTime));
}
CFTimeInterval GetClockWithBlock(dispatch_block_t block) {
clock_t currentTime = clock();
block();
clock_t lastTime = clock();
return (CFTimeInterval)(lastTime - currentTime)/CLOCKS_PER_SEC;
}
NSDate 、CFAbsoluteTimeGetCurrent、CACurrentMediaTime 的区别
字符串查找
__block NSString *testString = @"honzon now 25 years old, now live in beijing. honzon like watching moves, reading books and doing many other things.";
__block NSString *like = @"honzon";
NSLog(@"NSScanner used time: %f", GetCFAbsoluteTimeWithBlock(^{
NSScanner *scanner = [NSScanner scannerWithString:testString];
scanner.scanLocation = 0;
while (![scanner isAtEnd]) {
if ([scanner scanUpToString:like intoString:NULL]) {
NSLog(@"NSScanner success");
break;
}
scanner.scanLocation++;
}
}));
NSLog(@"rangeOfString used time: %f", GetCFAbsoluteTimeWithBlock(^{
if ([testString rangeOfString:like].length > 0) {
NSLog(@"rangeOfString success");
}
}));
NSLog(@"containsString used time: %f", GetCFAbsoluteTimeWithBlock(^{
//在iOS8以后，还可以用下面的方法来判断是否包含某字符串：
if ([testString containsString:like]) {
NSLog(@"containsString success");
}
}));
NSLog(@"NSPredicate used time: %f", GetCFAbsoluteTimeWithBlock(^{
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF CONTAINS %@",like];
if([predicate evaluateWithObject:testString]) {
NSLog(@"NSPredicate success");
}
}));
NSLog(@"NSTextCheckingResult used time: %f", GetCFAbsoluteTimeWithBlock(^{
NSError *error = NULL;
NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:like options:NSRegularExpressionCaseInsensitive error:&error];
NSTextCheckingResult *result = [regex firstMatchInString:testString options:0 range:NSMakeRange(0, [testString length])];
if (result) {
NSLog(@"NSTextCheckingResult success");
}
}));
NSLog(@"hasPrefix used time: %f", GetCFAbsoluteTimeWithBlock(^{
if ([testString hasPrefix:like]) {//hasSuffix
NSLog(@"hasPrefix success");
}
}));
//查找文字(honzon)位于最开始位置 containsString(0.000035) > hasPrefix(0.000042) > rangeOfString(0.000046) > NSPredicate(0.000385) > NSScanner(0.000808) > NSRegularExpression(0.003134)
//查找文字(like)位于最中间位置 containsString(0.000038) > rangeOfString(0.000061) > NSScanner(0.000887) > NSPredicate(0.000363) > NSRegularExpression(0.002953)
//查找文字(things.)位于最末端位置 containsString(0.000088) > hasSuffix(0.000089) > rangeOfString(0.000113) > NSPredicate(0.000416) > NSScanner(0.000841) > NSRegularExpression(0.003864)
在iOS8之前，可以尽量使用rangeOfString:方法来查找字符串，之后的话，使用containsString会更加快速。
