Merge pull request #1798 from corob-msft/cr-c2131

Add C2131 for DevDiv bug 803789

Author: v-shils

docs/error-messages/compiler-errors-1/TOC.md

@@ -232,6 +232,7 @@
 ## [Compiler Error C2128](compiler-error-c2128.md)
 ## [Compiler Error C2129](compiler-error-c2129.md)
 ## [Compiler Error C2130](compiler-error-c2130.md)
+## [Compiler Error C2131](compiler-error-c2131.md)
 ## [Compiler Error C2132](compiler-error-c2132.md)
 ## [Compiler Error C2133](compiler-error-c2133.md)
 ## [Compiler Error C2134](compiler-error-c2134.md)

docs/error-messages/compiler-errors-1/compiler-error-c2131.md

@@ -0,0 +1,40 @@
+---
+title: "Compiler Error C2131"
+ms.date: "02/28/2019"
+f1_keywords: ["C2131"]
+helpviewer_keywords: ["C2131"]
+---
+# Compiler Error C2131
+
+> expression did not evaluate to a constant
+
+An expression declared as **const** or **constexpr** didn't evaluate to a constant at compile time. The compiler must be able to determine the value of the expression at the point it's used.
+
+## Example
+
+This example shows a way to cause error C2131, and how to fix it.
+
+```cpp
+// c2131.cpp
+// compile by using: cl /EHsc /W4 /c c2131.cpp
+
+struct test
+{
+    static const int array_size; // To fix, init array_size here.
+    int size_array[array_size];  // C2131
+};
+
+const int test::array_size = 42;
+```
+
+```Output
+c2131.cpp
+c2131.cpp(7): error C2131: expression did not evaluate to a constant
+c2131.cpp(7): note: failure was caused by non-constant arguments or reference to a non-constant symbol
+c2131.cpp(7): note: see usage of 'array_size'
+```
+
+## See also
+
+[const](../../cpp/const-cpp.md)<br/>
+[constexpr](../../cpp/constexpr-cpp.md)<br/>

docs/error-messages/compiler-errors-1/compiler-errors-c2100-through-c2199.md

@@ -1,7 +1,7 @@
 ---
 title: "Compiler Errors C2100 through C2199"
 ms.date: "11/17/2017"
-f1_keywords: ["C2119", "C2123", "C2125", "C2126", "C2127", "C2131", "C2136", "C2176", "C2187", "C2189"]
+f1_keywords: ["C2119", "C2123", "C2125", "C2126", "C2127", "C2136", "C2176", "C2187", "C2189"]
 helpviewer_keywords: ["C2119", "C2123", "C2125", "C2126", "C2127", "C2131", "C2136", "C2176", "C2187", "C2189"]
 ms.assetid: 1ccab076-0954-4386-b959-d3112a6793ae
 ---
@@ -46,7 +46,7 @@ The articles in this section of the documentation explain a subset of the error
 |[Compiler Error C2128](compiler-error-c2128.md)|'*function*': alloc_text/same_seg applicable only to functions with C linkage|
 |[Compiler Error C2129](compiler-error-c2129.md)|static function '*identifier*' declared but not defined|
 |[Compiler Error C2130](compiler-error-c2130.md)|#line expected a string containing the filename, found '*token*'|
-|Compiler Error C2131|expression did not evaluate to a constant|
+|[Compiler Error C2131](compiler-error-c2131.md)|expression did not evaluate to a constant|
 |[Compiler Error C2132](compiler-error-c2132.md)|syntax error: unexpected identifier|
 |[Compiler Error C2133](compiler-error-c2133.md)|'*identifier*': unknown size|
 |[Compiler Error C2134](compiler-error-c2134.md)|'*function*': call does not result in a constant expression|