C/C中的strtod（）函数++-yiteyi-C++库

这个 斯特罗德（） 是C和C++ STL中的一个内置函数，它将字符串的内容解释为浮点数，并将其值作为一个值返回。它将指针设置为指向字符串最后一个有效字符后的第一个字符（仅当有有效字符时），否则将指针设置为null。

null

语法 :

double strtod(str, &end)

参数 : str ：指定以浮点数表示的字符串。终止：指定了一个参数，该参数指的是已分配的char*类型的对象。

返回值 ：如果无法执行有效转换，则返回双精度值（从字符串转换而来）和0。

以下程序说明了上述功能：

方案1 :

                     // C++ program to illustrate the                   
                     // strtod() function                   
                     #include <cstdlib>                   
                     #include <iostream>                   
                             
                     using                               namespace                               std;                   
                             
                     int                               main()                   
                     {                   
                                         char                               str[] =                               "11.03e 0mn"                               ;                   
                                         char                               * end;                   
                                         double                               number;                   
                             
                                         number =                               strtod                               (str, &end);                   
                                         cout <<                               "number = "                               << str << endl;                   
                                         cout <<                               "double = "                               << number << endl;                   
                                         cout <<                               "end string = "                               << end << endl;                   
                             
                                         return                               0;                   
                     }                   

输出：

number = 11.03e 0mn
double = 11.03
end string = e 0mn

方案2 :

                     // C++ program to illustrate the                   
                     // strtod() function without trailing characters                   
                     #include <cstdlib>                   
                     #include <iostream>                   
                             
                     using                               namespace                               std;                   
                             
                     int                               main()                   
                     {                   
                                         char                               str[] =                               "4.06"                               ;                   
                                         char                               * end;                   
                                         double                               number;                   
                             
                                         number =                               strtod                               (str, &end);                   
                                         cout <<                               "number= "                               << str << endl;                   
                                         cout <<                               "double= "                               << number << endl;                   
                             
                                         // If end is not Null                   
                                         if                               (*end) {                   
                                         cout << end;                   
                                         }                   
                                         // If end is Null                   
                                         else                               {                   
                                         cout <<                               "null"                               ;                   
                                         }                   
                                         return                               0;                   
                     }                   

输出：

number= 4.06
double= 4.06
null

方案3 : 具有指数和十六进制的strtod（）函数

                     // C++ program to illustrate the                   
                     // strtod() function with exponents and hexadecimals                   
                     #include <cstdlib>                   
                     #include <cstring>                   
                     #include <iostream>                   
                             
                     using                               namespace                               std;                   
                     int                               main()                   
                     {                   
                                         // initialize a exponential value                   
                                         char                               str[] =                               "-89.04e-3win gfg"                               ;                   
                                         char                               * end;                   
                                         double                               number;                   
                             
                                         number =                               strtod                               (str, &end);                   
                                         cout <<                               "str = "                               << str << endl;                   
                                         cout <<                               "double = "                               << number << endl;                   
                                         cout <<                               "end string = "                               << end << endl                   
                                         << endl;                   
                             
                                         // initialize a new hexadecimal value                   
                                         strcpy                               (str,                               "1998gupta.1204ishwar"                               );                   
                             
                                         number =                               strtod                               (str, &end);                   
                                         cout <<                               "str = "                               << str << endl;                   
                                         cout <<                               "double = "                               << number << endl;                   
                                         cout <<                               "end string = "                               << end << endl;                   
                             
                                         return                               0;                   
                     }                   

输出：

str = -89.04e-3win gfg
double = -0.08904
end string = win gfg

str = 1998gupta.1204ishwar
double = 1998
end string = gupta.1204ishwar

方案4 :

                     // C++ program to illustrate the                   
                     // strtod() function for Infinity and NaN                   
                     #include <cstdlib>                   
                     #include <iostream>                   
                             
                     using                               namespace                               std;                   
                             
                     int                               main()                   
                     {                   
                                         char                               * end;                   
                             
                                         cout <<                               "Infinity"                   
                                         <<                               " to double = "                   
                                         <<                               strtod                               (                               "infinity"                               , &end) << endl;                   
                                         cout <<                               "end string = "                               << end << endl                   
                                         << endl;                   
                             
                                         cout <<                               "Infpqrs"                   
                                         <<                               " to double = "                               <<                   
                                         strtod                               (                               "Infpqrs"                               , &end) << endl;                   
                                         cout <<                               "end string = "                               << end << endl                   
                                         << endl;                   
                             
                                         cout <<                               "NaN11x"                   
                                         <<                               " to double = "                   
                                         <<                               strtod                               (                               "NaN11x"                               , &end) << endl;                   
                                         cout <<                               "end string = "                               << end << endl                   
                                         << endl;                   
                             
                                         return                               0;                   
                     }                   

输出：

Infinity to double = inf
end string = 

Infpqrs to double = inf
end string = pqrs

NaN11x to double = nan
end string = 11x

项目5 : 带前导空格的strtod（）函数

                     // C++ program to illustrate the                   
                     // strtod() function with leading whitespace                   
                     #include <cstdlib>                   
                     #include <iostream>                   
                             
                     using                               namespace                               std;                   
                             
                     int                               main()                   
                     {                   
                                         char                               * end;                   
                             
                                         cout <<                               "99.99"                   
                                         <<                               " to double = "                   
                                         <<                               strtod                               (                               " 19.99"                               , &end) << endl;                   
                                         // end pointer is set to null                   
                                         cout <<                               "end string = "                   
                                         << end << endl                   
                                         << endl;                   
                             
                                         // Returns 0 because of invalid conversion                   
                                         cout <<                               "xyz1.80"                   
                                         <<                               " to double = "                   
                                         <<                               strtod                               (                               "xyz1.80"                               , &end) << endl;                   
                                         cout <<                               "end string = "                               << end << endl                   
                                         << endl;                   
                             
                                         return                               0;                   
                     }                   

输出：

99.99 to double = 19.99
end string = 

xyz1.80 to double = 0
end string = xyz1.80

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