C＃| Convert.ToDouble(String，IFormatProvider)方法

此方法用于使用指定的区域性特定格式信息将数字的指定字符串表示形式转换为等效的双精度浮点数。

句法：

public static double ToDouble (string value, IFormatProvider provider);

参数：

• value：它是一个包含要转换的数字的字符串。
• provider：提供者：提供特定于区域性的格式信息的对象。

返回值：该方法返回一个双精度浮点数，它等于value中的数字，如果value为null ，则返回0(零)。

例外情况：

• FormatException：如果该值不是有效格式的数字。
• OverflowException：如果该值表示一个小于MinValue或大于MaxValue的数字。

下面的程序说明了Convert.ToDouble(String，IFormatProvider)方法的用法：

范例1：

// C# program to demonstrate the
// Convert.ToDouble() Method
using System;
using System.Globalization;
  
class GFG {
  
// Main Method
public static void Main()
{
    try {
  
        // Create a NumberFormatInfo object 
        // and set some of its properties.
        NumberFormatInfo provider = new NumberFormatInfo();
        provider.NumberDecimalSeparator = ", ";
        provider.NumberGroupSeparator = ".";
        provider.NumberGroupSizes = new int[] { 3 };
  
        // declaring and initializing String array
        string[] values = {"123456789", "12345.6789",
                                      "12345, 6789"};
  
        // calling get() Method
        Console.Write("Converted decimal value "
                         + "of specified strings: ");
  
        for (int j = 0; j < values.Length; j++) 
        {
            get(values[j], provider);
        }
    }
  
    catch (FormatException e)
    {
  
        Console.WriteLine("\n");
        Console.Write("Exception Thrown: ");
        Console.Write("{0}", e.GetType(), e.Message);
    }
  
    catch (OverflowException e)
    {
  
        Console.WriteLine("\n");
        Console.Write("Exception Thrown: ");
        Console.Write("{0}", e.GetType(), e.Message);
    }
}
  
// Defining get() method
public static void get(string s,
      NumberFormatInfo provider)
{
  
    // converting string to specified char
    double val = Convert.ToDouble(s, provider);
  
    // display the converted char value
    Console.Write(" {0}, ", val);
}
}

输出：

Converted decimal value of specified strings:  123456789,  123456789,  12345.6789,

示例2：对于FormatException

// C# program to demonstrate the
// Convert.ToDouble() Method
using System;
using System.Globalization;
  
class GFG {
  
// Main Method
public static void Main()
{
    try {
  
        // Create a NumberFormatInfo object 
        // and set some of its properties.
        NumberFormatInfo provider = new NumberFormatInfo();
        provider.NumberDecimalSeparator = ", ";
        provider.NumberGroupSeparator = ".";
        provider.NumberGroupSizes = new int[] { 3 };
  
        // declaring and initializing String array
        string[] values = {"123456789", "12345.6789",
                                      "12345, 6789"};
  
        // calling get() Method
        Console.Write("Converted double value"
                 + " of specified strings: ");
  
        for (int j = 0; j < values.Length; j++)
        {
  
            get(values[j], provider);
        }
  
        Console.WriteLine("\n");
        string s = "123 456, 789";
  
        Console.WriteLine("format of s is invalid ");
  
        // converting string to specified char
        double val = Convert.ToDouble(s, provider);
  
        // display the converted char value
        Console.Write(" {0}, ", val);
    }
  
    catch (FormatException e) 
    {
  
        Console.Write("Exception Thrown: ");
        Console.Write("{0}", e.GetType(), e.Message);
    }
      
    catch (OverflowException e) 
    {
  
        Console.Write("Exception Thrown: ");
        Console.Write("{0}", e.GetType(), e.Message);
    }
}
  
// Defining get() method
public static void get(string s,
      NumberFormatInfo provider)
{
  
    // converting string to specified char
    double val = Convert.ToDouble(s, provider);
  
    // display the converted char value
    Console.Write(" {0}, ", val);
}
}

输出：

Converted double value of specified strings:  123456789,  123456789,  12345.6789, 

format of s is invalid 
Exception Thrown: System.FormatException

示例3：对于OverflowException

// C# program to demonstrate the
// Convert.ToDouble() Method
using System;
using System.Globalization;
  
class GFG {
  
// Main Method
public static void Main()
{
    try {
  
        // Create a NumberFormatInfo object
        // and set some of its properties.
        NumberFormatInfo provider = new NumberFormatInfo();
        provider.NumberDecimalSeparator = ", ";
        provider.NumberGroupSeparator = ".";
        provider.NumberGroupSizes = new int[] { 3 };
  
        // declaring and initializing String array
        string[] values = { "123456789", "12345.6789",
                                      "12345, 6789" };
  
        // calling get() Method
        Console.Write("Converted decimal value "
                    + "of specified strings: ");
  
        for (int j = 0; j < values.Length; j++)
        {
  
            get(values[j], provider);
        }
  
        Console.WriteLine("\n");
        string s = "-7922816251426433759354395033500000";
  
        Console.WriteLine("s is less than the MaxValue");
  
        // converting string to specified char
        decimal val = Convert.ToDecimal(s, provider);
  
        // display the converted char value
        Console.Write(" {0}, ", val);
    }
      
    catch (FormatException e) 
    {
        Console.Write("Exception Thrown: ");
        Console.Write("{0}", e.GetType(), e.Message);
    }
      
    catch (OverflowException e) 
    {
        Console.Write("Exception Thrown: ");
        Console.Write("{0}", e.GetType(), e.Message);
    }
}
  
// Defining get() method
public static void get(string s,
      NumberFormatInfo provider)
{
  
    // converting string to specified char
    double val = Convert.ToDouble(s, provider);
  
    // display the converted char value
    Console.Write(" {0}, ", val);
}
}

输出：

Converted decimal value of specified strings:  123456789,  123456789,  12345.6789, 

s is less than the MaxValue
Exception Thrown: System.OverflowException

参考：

• https://docs.microsoft.com/zh-cn/dotnet/api/system.convert.todouble?view=netframework-4.7.2#System_Convert_ToDouble_System_String_System_IFormatProvider_