Fix #7515 FN stlcstrStream with std::cout (#8040)

Author: chrchr-github

lib/checkstl.cpp

@@ -2082,7 +2082,7 @@ void CheckStl::string_c_str()
                     const Token* strm = tok;
                     while (Token::simpleMatch(strm, "<<"))
                         strm = strm->astOperand1();
-                    if (strm && strm->variable() && strm->variable()->isStlType())
+                    if (strm && ((strm->variable() && strm->variable()->isStlType()) || Token::Match(strm->tokAt(-1), "std :: cout|cerr")))
                         string_c_strStream(tok);
                 }
             }

test/teststl.cpp

@@ -4568,6 +4568,14 @@ class TestStl : public TestFixture {
                       "[test.cpp:14:10]: (performance) Passing the result of c_str() to a stream is slow and redundant. [stlcstrStream]\n",
                       errout_str());
 
+        check("void f(const std::string& s) {\n"
+              "    std::cout << s.c_str();\n"
+              "    std::cerr << s.c_str();\n"
+              "}\n");
+        ASSERT_EQUALS("[test.cpp:2:15]: (performance) Passing the result of c_str() to a stream is slow and redundant. [stlcstrStream]\n"
+                      "[test.cpp:3:15]: (performance) Passing the result of c_str() to a stream is slow and redundant. [stlcstrStream]\n",
+                      errout_str());
+
         check("struct S { std::string str; };\n"
               "struct T { S s; };\n"
               "struct U { T t[1]; };\n"