c语言中向文本文件、二进制文件中写入实数

c语言向文本文件、二进制文件中写入实数。

1、

#include <stdio.h>

int main(void)
{
    FILE *fp;
    double pi = 3.14159265358979323846;
    printf("pi from value: %23.21f.
", pi);  // 因为浮点数精度有限，不能准确显示数值
    
    if((fp = fopen("PI.txt", "w")) == NULL)
        printf("aFile open failed.
");
    else
    {
        fprintf(fp, "%f", pi);   // fprintf写入文件，默认保留6位有效小数
        fclose(fp);
    }
    
    if((fp = fopen("PI.txt", "r")) == NULL)
        printf("aFile open failed.
");
    else
    {
        fscanf(fp, "%lf", &pi);
        printf("pi from file: %23.21f.
", pi);  // double型不能准确无误的显示所有位数
        fclose(fp);
    }
    return 0;
}

2、

#include <stdio.h>

int main(void)
{
    FILE *fp;
    double pi = 3.14159265358979323846;
    printf("pi from value: %23.21f.
", pi); // 因为浮点数的精度有限，与变量值不一致 
    
    if((fp = fopen("PI.bin", "w")) == NULL)
        printf("aFile open failed.
");  
    else
    {
        fwrite(&pi, sizeof(double), 1, fp);  // 将变量pi以二进制形式写入文件 
        fclose(fp);    
    }    
    
    if((fp = fopen("PI.bin", "r")) == NULL)
        printf("aFile open failed.
");
    else
    {
        fread(&pi, sizeof(double), 1, fp);  //以二进制形式读取文件 
        printf("pi from file: %23.21f.
", pi); // 显示变量，变量和写入的变量没有差异， 
        fclose(fp);    
    } 
    return 0;
}