C語言-轉化字符串為雙精度浮點數(包括對科學計數法的處理)的函數atof

//寫一個把字符串轉換為浮點數的程序
#include <ctype.h>
#include <stdlib.h> //這個頭文件里含有atof的標准庫函數聲明

double atof2(char s[]){
    double res; int i; int sign = 1;
    double fpart = 1.0;
    double exp = 10;
    int expNum = 1;
    double n = 1.0;
    //讀掉字符串前面可能有的空格
    for (i = 0; isspace(s[i]); i++)
        ;
    //讀取正負的標識
    if (s[i] == '-'){
        sign = -1;
        i++;//把指針遞增放在分支里，以免在判斷不成功時向后移動
    }
    for(res = 0.0 ; isdigit(s[i]); i++){
        res = res * 10.0 + ((int)s[i] - '0');
    }
    if (s[i++] == '.'){
        for (fpart = 1.0; isdigit(s[i]); i++){
            res = res * 10.0 + ((int)s[i] - '0');
            fpart *= 10.0;
        }
    }
    if (s[i++] == e){
        if (s[i] == '-'){
            exp = 0.1;
            i++;
        }
        expNum = atoi((s + i))
    　　while (expNum-- > 0){
        　　n *= exp; 
    　　}
    }
    res = res * sign / fpart * n;
    return res;
}

2021-06-1616:48:07 BY PeaceCoder