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c# float和double的“坑”

2024-07-09 17:25:33   227人阅读

定义一个float类型的变量=0.7，结果在IL中却是0.69999999。

乘以10之后，获取整数值。得到的却是6。通过查看IL，竟然被转换成double类型再转换。就变成6了。

Demo:

QQ截图20140626123829

IL:

.method private hidebysig static void  Main(string[] args) cil managed{  .entrypoint  // 代码大小       93 (0x5d)  .maxstack  2  //定义变量  .locals init ([0] float32 val,           [1] int32 i)  IL_0000:  nop  IL_0001:  ldc.r4     0.69999999  //将0.69999999赋值给第0个变量。明明定义的是0.7  IL_0006:  stloc.0  IL_0007:  ldc.i4.s   10  /将10赋值给第一个变量  IL_0009:  stloc.1  //double类型的0.7  IL_000a:  ldc.r8     0.69999999999999996  IL_0013:  ldloc.1  IL_0014:  conv.r8  IL_0015:  mul  IL_0016:  call       float64 [mscorlib]System.Math::Floor(float64)  IL_001b:  call       void [mscorlib]System.Console::WriteLine(float64)  IL_0020:  nop  IL_0021:  ldloc.0  IL_0022:  call       void [mscorlib]System.Console::WriteLine(float32)  IL_0027:  nop  //从堆栈中加载出val  IL_0028:  ldloc.0  //从堆栈中加载出i  IL_0029:  ldloc.1  //将i转换为float类型  IL_002a:  conv.r4  //val*i  IL_002b:  mul  //将乘法运算之后的结果转换为double类型  IL_002c:  conv.r8  //调用Math.Floor对运算后的结果处理  IL_002d:  call       float64 [mscorlib]System.Math::Floor(float64)  IL_0032:  call       void [mscorlib]System.Console::WriteLine(float64)  IL_0037:  nop  IL_0038:  ldloc.0  IL_0039:  conv.r8  IL_003a:  call       void [mscorlib]System.Console::WriteLine(float64)  IL_003f:  nop  IL_0040:  ldloc.0  IL_0041:  ldloc.1  IL_0042:  conv.r4  IL_0043:  mul  IL_0044:  conv.r8  IL_0045:  call       void [mscorlib]System.Console::WriteLine(float64)  IL_004a:  nop  IL_004b:  ldloc.0  IL_004c:  conv.r8  IL_004d:  ldloc.1  IL_004e:  conv.r8  IL_004f:  mul  IL_0050:  call       void [mscorlib]System.Console::WriteLine(float64)  IL_0055:  nop  IL_0056:  call       string [mscorlib]System.Console::ReadLine()  IL_005b:  pop  IL_005c:  ret} // end of method Program::Main


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