fscanf和fprintf为C程序中的文本文件更改的值[重复]

This question already has an answer here:

这个问题在这里已有答案：

• What range of numbers can be represented in a 16-, 32- and 64-bit IEEE-754 systems? 7 answers
• 在16位，32位和64位IEEE-754系统中可以表示哪些数字？ 7个答案

I would like to output like "correct output data" from "input data" by below C program. But the result shows that the values are changed like "actual output data". Let me know how to solve it.

我想通过下面的C程序从“输入数据”输出“正确的输出数据”。但结果显示值的变化类似于“实际输出数据”。让我知道如何解决它。

input data
-5190.978 -90026.901 158.677 15 90 81 58
-5165.821 -90011.875 152.742 15 90 89 54
-5158.762 -90010.093 148.083 31 80 82 42

输入数据-5190.978 -90026.901 158.677 15 90 81 58 -5165.821 -90011.875 152.742 15 90 89 54 -5158.762 -90010.093 148.083 31 80 82 42

correct output data
-5190.978 -90026.901 158.677 90 81 58
-5165.821 -90011.875 152.742 90 89 54
-5158.762 -90010.093 148.083 80 82 42

正确的输出数据-5190.978 -90026.901 158.677 90 81 58 -5165.821 -90011.875 152.742 90 89 54 -5158.762 -90010.093 148.083 80 82 42

actual output data
-5190.978 -90026.898 158.677 90 81 58
-5165.821 -90011.875 152.742 90 89 54
-5158.762 -90010.094 148.083 80 82 42

实际产量数据-5190.978 -90026.898 158.677 90 81 58 -5165.821 -90011.875 152.742 90 89 54 -5158.762 -90010.094 148.083 80 82 42

/***************************************************************************:::
 xyz(ref)rgb2xyzrgb
    19/08/2016
 ver1.1 2009/3/7
 *******************************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

int main(int argc,char *argv[])
{

    FILE *fpr,*fpw;
    int ref,r,g,b;
    float x,y,z;
    float n_x,n_y,n_z;

    /*****************************************************
         2.command line arguments processing
    *******************************************************/
    if(argc!=3)
    {
            fprintf(stderr,"Usage: %s (1)input_org.txt\n(2)write_xyz FILENAME\n",argv[0]);
            exit(1);
    }
    printf("OPEN FILE NAME:%s\n",argv[1]);

        /**********************************************************************************
         **********************************************************************************
         4.  FILE OPEN + Binary File Input
         **********************************************************************************
         *************************************************************************************/

    // open input file
    if((fpr=fopen(argv[1],"rt"))==NULL)
    {
        printf("file cannot be opened。\n");
        exit(1);
    }

    //write file
    if((fpw=fopen(argv[2],"wt"))==NULL)
    {
        fprintf(stderr,"DSM by GSI data.raw\n");
        exit(1);
    }

    while (fscanf(fpr,"%f %f %f %d %d %d %d", &x,&y,&z,&ref,&r,&g,&b) != EOF)
    {
        //printf("%.3f %.3f %.3f %d %d %d\n",x,y,z,r,g,b);
        n_x = roundf(x * 1000) / 1000;
        n_y = roundf(y * 1000) / 1000;
        n_z = roundf(z * 1000) / 1000;
        //printf("%.3f %.3f %.3f %d %d %d\n",n_x,n_y,n_z,r,g,b);        
        fprintf(fpw,"%.3f %.3f %.3f %d %d %d\n",n_x,n_y,n_z,r,g,b);
            //printf("x:%f y:%f z:%f\n", x,y,z);
    }

    fclose(fpr);
    fclose(fpw);

}

1 个解决方案

#1

Instead of -90026.901 computer stores the nearest number that fits the precision. It's 90026.898. Remember that numbers are stored in binary on computers and 901/1000 doesn't have finite binary form. For this reason, some of the precision will be cut.

而不是-90026.901计算机存储最接近精度的数字。这是90026.898。请记住，数字在计算机上以二进制形式存储，而901/1000不具有有限的二进制形式。因此，一些精度将被削减。

It would be the same if you tried to print 1/3. It won't print all the digits, but you actually expect it as you're used to decimal system. In binary system, some of the fractions that have finite decimal form won't have one.

如果您尝试打印1/3，它将是相同的。它不会打印所有数字，但实际上你会习惯它，因为你习惯了十进制系统。在二进制系统中，一些具有有限小数形式的分数将不具有一个。

The solution? Always try to enlarge macheps which is the arithmetic precision. The easiest would be to use double instead of float. It still doesn't give 100% but it's more probable that will work.

解决方案？总是尝试放大算术精度的macheps。最简单的方法是使用double而不是float。它仍然没有给出100％，但它更有可能会起作用。

The topic is known as scientific calculation and is pain in a** for programmers.

这个主题被称为科学计算，对程序员来说是痛苦的。