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dingzs3
V2EX  ›  程序员

strtod 转化异常

  •  
  •   dingzs3 · Oct 17, 2018 · 2256 views
    This topic created in 2776 days ago, the information mentioned may be changed or developed.

    读取两行 double 数字:

    0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

    0 0 0 0 0 0 0 0 0 0 0 0.02 0.12 0.12 0.1 0.18 0.2 0.24 0.32 0.26 0.18 0.14 0.04 0.04 0.02 0.02 0 0 0 0 0 0 0 0 0 0 0 0 0 0

    代码:

    ptr=strtok(line," ");

    if(ptr == NULL)

    continue;
    

    while(ptr != NULL) {

    num = strtod(ptr,NULL);
    
    kd_ljj.x[row][col]=num;
    
    printf("row=%d col=%d num=%lf\n",row,col,num);
    
    row++;
    
    ptr=strtok(NULL," ");
    

    }

    读取完成后,为啥用 gdb 看到的是这样的:

    (gdb) p kd_ljj.x

    $1 = {{0, 0} <repeats 11 times>, {0, 0.02}, {0, 0.12}, {0, 0.12}, {0,

    0.10000000000000001}, {0, 0.17999999999999999}, {0, 0.20000000000000001}, {0,

    0.23999999999999999}, {0, 0.32000000000000001}, {0, 0.26000000000000001}, {0, 0.17999999999999999}, {0,

    0.14000000000000001}, {0, 0.040000000000000001}, {0, 0.040000000000000001}, {0, 0.02},
    {0, 0.02}, {0, 
    0} <repeats 14 times>}
    

    为什么中间的数字会出现偏差,而 printf 打印的又是正常的,这个是代码的问题还是什么原因

    2 replies    2018-10-18 13:42:45 +08:00
    ejq
        1
    ejq  
       Oct 17, 2018 via Android   ❤️ 1
    浮点数误差了解一下

    IEEE 754 了解一下

    https://0.30000000000000004.com
    dingzs3
        2
    dingzs3  
    OP
       Oct 18, 2018
    多谢啊
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