C# Convert.ToDouble(String, IFormatProvider)用法及代碼示例

此方法用於使用指定的區域性特定格式信息將數字的指定字符串表示形式轉換為等效的雙精度浮點數。

用法:

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

參數：

value:它是一個包含要轉換的數字的字符串。
provider:它是提供區域性特定格式信息的對象。

返回值：此方法返回一個雙精度浮點數，它等於value中的數字，如果value為null，則返回0(零)。

異常：

FormatException：如果該值不是有效格式的數字。
OverflowException：如果該值表示一個小於MinValue或大於MaxValue的數字。

以下示例程序旨在說明Convert.ToDouble(String，IFormatProvider)方法的用法：

範例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); 
} 
}

輸出：

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

範例2：對於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); 
} 
}

輸出：

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

format of s is invalid 
Exception Thrown:System.FormatException

範例3：對於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); 
} 
}

輸出：

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

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

參考：

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

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