Question

I need to put out a double value into an file. So for all my other string i have to put out i use fputs because i think and timed it that fputs is faster then fprintf.

但是,如果想阐明双重价值,那么就能够用手法来做,这样就尝试了print。这非常缓慢。我需要更多的时间,才能取代印本,并用数字(TEST)文档;

怎么能够像扼杀那样迅速翻开两番。是否需要首先将其转化为扼杀?

我发现有些转换。但是,如果使用这些产品,那么使用这些产品的速度就很慢。

那么,如果把双双双双 the放在档案中,怎么能够如此迅速?

  fputs("TEST",fileout); //FAST
  fprintf(fileout, "%f",p); //SLOW

EDIT:

印有两倍的时段:

END.PROCESSING.DATA: 2013-04-26 08:10:33.000
END.CALC.IN.FILE: 2013-04-26 08:11:13.000

• 时段:

END.PROCESSING.DATA: 2013-04-26 08:14:10.000
END.CALC.IN.FILE: 2013-04-26 08:14:37.000

当时的法律:

now = time (0);
strftime (buff, 100, "%Y-%m-%d %H:%M:%S.000", localtime (&now));
printf ("END.PROCESSING.DATA: %s
", buff);

//output file
FILE *fileout;
fileout = fopen("out.txt","w");
double p;
for(i=0; i<17000;i++){
  for(j=0; j<i;j++){
    for(z=0;z<400;z++){
      //DO SOME WORK
    }
    p = 1.0;
    fputs(allsubsts[i],fileout);
    fputs(";",fileout);
    fputs(allsubsts[j],fileout);
    fputs(";",fileout);
    //fprintf(fileout, "%.21g", p);
    fputs("TEST",fileout);
    fputs(";
",fileout);
  }
}
fclose(fileout);

now = time(0);
strftime(buff,100,"%Y-%m-%d %H:%M:%S.000", localtime(&now));
printf("END.CALC.IN.FILE: %s
",buff);

Changes between the time are only the change that i put the double instead the TEST string in the file.

Answer 1

Converting a floating point number to a decimal representation is a fundamentally slow operation. You might try using the %a specifier instead of %f to store it as a hex float; this should be much faster and would safely preserve the original value rather than a poor approximation. If you need decimal, you should be using %.21g or similar, not %f, as the latter will lose most of the precision.

如果对你来说,所有这一切都不够快,那么你很可能需要直接节省双亲的代表性。

Answer 2

You can use C++17 std::to_char or C++20 std::format to speed up floating-point output by first formatting the number into a buffer and then writing it out:

char buf[32];
char* end = std::format_to(buf, "{}", n);
*end =   ;
fputs(buf, file);

这些方法不使用当地法,通常使用更快的算法将双平浮动点转换为正式代表点。

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