问题描述
[Key]
public int DonationId { get; set; }
public DateTime? TransacTime { get; set; }
public int Amount { get; set; }
public string IC { get; set; }
[ForeignKey("IC")]
public Customers Customers { get; set; }
主机:Win10 x64。
结果:
案例1。
$ clang t2.c -o t2.clang.exe && ./t2.clang.exe FE_DOWNWARD 0x1.8814e60000000p+5 [0x42440a73] 0 FE_TONEAREST 0x1.8814e60000000p+5 [0x42440a73] 0 FE_TOWARDZERO 0x1.8814e60000000p+5 [0x42440a73] 0 FE_UPWARD 0x1.8814e60000000p+5 [0x42440a73] 0 $ clang --version clang version 8.0.1 (tags/RELEASE_801/final)
案例2。
$ gcc t2.c -o t2.gcc.exe && ./t2.gcc.exe FE_DOWNWARD 0x1.8814e60000000p+5 [0x42440a73] 0 FE_TONEAREST 0x1.8814e60000000p+5 [0x42440a73] 0 FE_TOWARDZERO 0x1.8814e60000000p+5 [0x42440a73] 0 FE_UPWARD 0x1.8814e60000000p+5 [0x42440a73] 0 $ gcc --version gcc (GCC) 10.2.0
情况3。
cl t2.c && t2 Microsoft (R) C/C++ Optimizing Compiler Version 19.25.28611 for x64 ... FE_DOWNWARD 0x1.8814e40000000p+5 [0x42440a72] 0 FE_TONEAREST 0x1.8814e60000000p+5 [0x42440a73] 0 FE_TOWARDZERO 0x1.8814e40000000p+5 [0x42440a72] 0 FE_UPWARD 0x1.8814e60000000p+5 [0x42440a73] 0
案例4。
cl t2.c && t2 Microsoft (R) C/C++ Optimizing Compiler Version 19.25.28611 for x86 ... The system cannot execute the specified program. Pop-up window appears: "Virus & thread protection: Windows Defender Antivirus found threats. Get details."
案例5。
wandbox.org: gcc HEAD 11.0.0 20200 $ gcc prog.c -Wall -Wextra -std=c99 "-lm" FE_DOWNWARD 0x1.8814e40000000p+5 [0x42440a72] 0 FE_TONEAREST 0x1.8814e60000000p+5 [0x42440a73] 0 FE_TOWARDZERO 0x1.8814e40000000p+5 [0x42440a72] 0 FE_UPWARD 0x1.8814e60000000p+5 [0x42440a73] 0
案例6。
wandbox.org: clang HEAD 12.0.0 $ clang prog.c -Wall -Wextra -std=gnu11 "-lm" FE_DOWNWARD 0x1.8814e40000000p+5 [0x42440a72] 0 FE_TONEAREST 0x1.8814e60000000p+5 [0x42440a73] 0 FE_TOWARDZERO 0x1.8814e40000000p+5 [0x42440a72] 0 FE_UPWARD 0x1.8814e60000000p+5 [0x42440a73] 0
问题:
- 为什么编译器之间的结果(
#include <stdio.h> #include <stdint.h> #include <fenv.h> #include <math.h> int main() { typedef union { uint32_t u; float f; } ufloat; ufloat val; float arg = 2401.999999; int r; r = fesetround(FE_DOWNWARD); val.f = sqrtf(arg); printf ("FE_DOWNWARD %22.13a [0x%x] %d\n",val.f,val.u,r); r = fesetround(FE_TONEAREST); val.f = sqrtf(arg); printf ("FE_TONEAREST %22.13a [0x%x] %d\n",r); r = fesetround(FE_TOWARDZERO); val.f = sqrtf(arg); printf ("FE_TOWARDZERO %22.13a [0x%x] %d\n",r); r = fesetround(FE_UPWARD); val.f = sqrtf(arg); printf ("FE_UPWARD %22.13a [0x%x] %d\n",r); return 0; }
和0x42440a72
)不同? - 如何在编译器之间获得相同的结果?
解决方法
为什么编译器之间会有不同的结果(0x42440a72与0x42440a73)?
至少对于较早的gcc,不需要<fenv.h>
支持。
请参见floating-point environment access in <fenv.h>,Library feature,no compiler support required.
当我使用“ GNU C11(GCC)版本9.3.0(x86_64-pc-cygwin)”进行编译时,以下内容
#include <fenv.h>
#pragma STDC FENV_ACCESS ON
我收到以下信息:
warning: ignoring #pragma STDC FENV_ACCESS [-Wunknown-pragmas]
另请参见If pragma STDC FENV_ACCESS is absent,does it mean default rounding mode?,pragma STDC FENV_ACCESS ON is not supported
如何在编译器之间获得相同的结果?
没什么帮助,但不要使用fenv.h
的可选功能或避免选择编译器。
可能存在一个gcc编译时标志来提供帮助,但我不知道一个。
也使用#pragma STDC FENV_ACCESS ON
@Eric Postpischil。这可能无法解决此问题,但可以防止相关问题。