请问一下，如何设计一个循环，让假如循环执行的时间过长，就自动跳出循环?

_故事的小黄花_ 2016-07-22 09:03:51

就比如，while循环，要是条件一直满足，就会始终在while循环里执行，这样程序比较容易跑死。

我想，是不是可以在while循环里，添加一些什么样的代码，起到计时的作业。

不需要能计算精确的时间，只需要大致的时间。

一开始我想，用 i ++ 来计数，当 i 超过一个数值，就执行 break 语句，跳出循环。

但是这个也太不精确了吧，毕竟我们无法得知，系统进行一次 i ++ 运算的时间是多久。

所以请问各位大神，有没有什么好办法啊？

只限于 C 语言。不能用 C++

谢谢各位

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赵4老师 2016-07-25

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仅供参考：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#ifdef WIN32
    #include <windows.h>
    #include <io.h>
    #include <process.h>
    #define  MYVOID             void
#else
    #include <unistd.h>
    #include <sys/time.h>
    #include <pthread.h>
    #define  CRITICAL_SECTION   pthread_mutex_t
    #define  _vsnprintf         vsnprintf
    #define  MYVOID             void *
#endif
//Log{
#define MAXLOGSIZE 20000000
#define ARRSIZE(x) (sizeof(x)/sizeof(x[0]))
#include <time.h>
#include <sys/timeb.h>
#include <stdarg.h>
char logfilename1[]="MyLog1.log";
char logfilename2[]="MyLog2.log";
char logstr[16000];
char datestr[16];
char timestr[16];
char mss[4];
CRITICAL_SECTION cs_log;
FILE *flog;
#ifdef WIN32
void Lock(CRITICAL_SECTION *l) {
    EnterCriticalSection(l);
}
void Unlock(CRITICAL_SECTION *l) {
    LeaveCriticalSection(l);
}
void sleep_ms(int ms) {
    Sleep(ms);
}
#else
void Lock(CRITICAL_SECTION *l) {
    pthread_mutex_lock(l);
}
void Unlock(CRITICAL_SECTION *l) {
    pthread_mutex_unlock(l);
}
void sleep_ms(int ms) {
    usleep(ms*1000);
}
#endif
void LogV(const char *pszFmt,va_list argp) {
    struct tm *now;
    struct timeb tb;


    if (NULL==pszFmt||0==pszFmt[0]) return;
    if (-1==_vsnprintf(logstr,ARRSIZE(logstr),pszFmt,argp)) logstr[ARRSIZE(logstr)-1]=0;
    ftime(&tb);
    now=localtime(&tb.time);
    sprintf(datestr,"%04d-%02d-%02d",now->tm_year+1900,now->tm_mon+1,now->tm_mday);
    sprintf(timestr,"%02d:%02d:%02d",now->tm_hour     ,now->tm_min  ,now->tm_sec );
    sprintf(mss,"%03d",tb.millitm);
    printf("%s %s.%s %s",datestr,timestr,mss,logstr);
    flog=fopen(logfilename1,"a");
    if (NULL!=flog) {
        fprintf(flog,"%s %s.%s %s",datestr,timestr,mss,logstr);
        if (ftell(flog)>MAXLOGSIZE) {
            fclose(flog);
            if (rename(logfilename1,logfilename2)) {
                remove(logfilename2);
                rename(logfilename1,logfilename2);
            }
            flog=fopen(logfilename1,"a");
            if (NULL==flog) return;
        }
        fclose(flog);
    }
}
void Log(const char *pszFmt,...) {
    va_list argp;

    Lock(&cs_log);
    va_start(argp,pszFmt);
    LogV(pszFmt,argp);
    va_end(argp);
    Unlock(&cs_log);
}
//Log}
int No_Loop=0;
MYVOID testThread(void *pcn) {
    int n,i;

    n=(int)pcn;
    i=0;
    while (1) {
        sleep_ms(1000);
        Log("in testThread %d:i==%ds\n",n,++i);
        if (i>=5) No_Loop=1;
    }
}
int main(int argc,char * argv[]) {
    int i;
#ifdef WIN32
    InitializeCriticalSection(&cs_log);
#else
    pthread_mutex_init(&cs_log,NULL);
    pthread_t threads[1];
    int threadsN;
    int rc;
#endif
    Log("=========BEGIN==================\n");
#ifdef WIN32
    _beginthread((void(__cdecl *)(void *))testThread,0,(void *)1);
#else
    threadsN=0;
    rc=pthread_create(&(threads[threadsN++]),NULL,testThread,(void *)1);if (rc) Log("%d=pthread_create %d error!\n",rc,threadsN-1);
#endif
    i=0;
    while (1) {
        sleep_ms(100);
        Log("in main:i==%d\n",++i);
        if (No_Loop==1) break;//
    }
    Log("=========END====================\n");
#ifdef WIN32
    DeleteCriticalSection(&cs_log);
#else
    pthread_mutex_destroy(&cs_log);
#endif
    return 0;
}
//2012-06-14 16:27:21.500 =========BEGIN==================
//2012-06-14 16:27:21.609 in main:i==1
//2012-06-14 16:27:21.718 in main:i==2
//2012-06-14 16:27:21.828 in main:i==3
//2012-06-14 16:27:21.937 in main:i==4
//2012-06-14 16:27:22.046 in main:i==5
//2012-06-14 16:27:22.156 in main:i==6
//2012-06-14 16:27:22.265 in main:i==7
//2012-06-14 16:27:22.375 in main:i==8
//2012-06-14 16:27:22.484 in main:i==9
//2012-06-14 16:27:22.500 in testThread 1:i==1s
//2012-06-14 16:27:22.593 in main:i==10
//2012-06-14 16:27:22.703 in main:i==11
//2012-06-14 16:27:22.812 in main:i==12
//2012-06-14 16:27:22.921 in main:i==13
//2012-06-14 16:27:23.031 in main:i==14
//2012-06-14 16:27:23.140 in main:i==15
//2012-06-14 16:27:23.250 in main:i==16
//2012-06-14 16:27:23.359 in main:i==17
//2012-06-14 16:27:23.468 in main:i==18
//2012-06-14 16:27:23.500 in testThread 1:i==2s
//2012-06-14 16:27:23.578 in main:i==19
//2012-06-14 16:27:23.687 in main:i==20
//2012-06-14 16:27:23.796 in main:i==21
//2012-06-14 16:27:23.906 in main:i==22
//2012-06-14 16:27:24.015 in main:i==23
//2012-06-14 16:27:24.125 in main:i==24
//2012-06-14 16:27:24.234 in main:i==25
//2012-06-14 16:27:24.343 in main:i==26
//2012-06-14 16:27:24.453 in main:i==27
//2012-06-14 16:27:24.500 in testThread 1:i==3s
//2012-06-14 16:27:24.562 in main:i==28
//2012-06-14 16:27:24.671 in main:i==29
//2012-06-14 16:27:24.781 in main:i==30
//2012-06-14 16:27:24.890 in main:i==31
//2012-06-14 16:27:25.000 in main:i==32
//2012-06-14 16:27:25.109 in main:i==33
//2012-06-14 16:27:25.218 in main:i==34
//2012-06-14 16:27:25.328 in main:i==35
//2012-06-14 16:27:25.437 in main:i==36
//2012-06-14 16:27:25.500 in testThread 1:i==4s
//2012-06-14 16:27:25.546 in main:i==37
//2012-06-14 16:27:25.656 in main:i==38
//2012-06-14 16:27:25.765 in main:i==39
//2012-06-14 16:27:25.875 in main:i==40
//2012-06-14 16:27:25.984 in main:i==41
//2012-06-14 16:27:26.093 in main:i==42
//2012-06-14 16:27:26.203 in main:i==43
//2012-06-14 16:27:26.312 in main:i==44
//2012-06-14 16:27:26.421 in main:i==45
//2012-06-14 16:27:26.500 in testThread 1:i==5s
//2012-06-14 16:27:26.531 in main:i==46
//2012-06-14 16:27:26.531 =========END====================

ooolinux 2016-07-23

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Windows 可以用 GetTickCount，循环之前GetTickCount 作为初值，循环中每个循环GetTickCount 减初值来判断是否超时，单位是毫秒。

Crashdown 2016-07-22

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5楼说的对，可以直接调用库函数clock()，头文件time.h

lm_whales 2016-07-22

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0.01 秒时间太小了，不然的话，Windows 可以用定时器，可以大致保持精确 C,C++ 直接计时，可以用库函数 clock,time Windows 还可以用 API GetTickCount X86系列可以用 RDSTC指令有传说RDSTC指令　不够准确，可以改成这么用 Windows 用 QueryPerformanceCounter 和 QueryPerformanceFrequency， Linux 下用 POSIX 的 clock_gettime 函数，以 CLOCK_MONOTONIC 参数调用　不过　QueryPerformanceCounter　实际上就是对RDSTC指令的某种封装可能内部做了处理