ValueFlow: Improved handling of strings

lib/valueflow.cpp

@@ -374,12 +374,29 @@ static void valueFlowNumber(TokenList *tokenlist)
 
 static void valueFlowString(TokenList *tokenlist)
 {
+    std::map<unsigned int, const Token *> constantStrings;
+
     for (Token *tok = tokenlist->front(); tok; tok = tok->next()) {
         if (tok->type() == Token::eString) {
             ValueFlow::Value strvalue;
             strvalue.tokvalue = tok;
             setTokenValue(tok, strvalue);
         }
+
+        if (Token::Match(tok, "const char %var% [ %num%| ] = %str% ;")) {
+            const Token *vartok = tok->tokAt(2);
+            const Token *strtok = tok->linkAt(3)->tokAt(2);
+            constantStrings[vartok->varId()] = strtok;
+        }
+
+        if (tok->varId() > 0U) {
+            const std::map<unsigned int, const Token *>::const_iterator it = constantStrings.find(tok->varId());
+            if (it != constantStrings.end()) {
+                ValueFlow::Value strvalue;
+                strvalue.tokvalue = it->second;
+                setTokenValue(tok, strvalue);
+            }
+        }
     }
 }
 
@@ -1337,6 +1354,27 @@ static void execute(const Token *expr,
         execute(expr->astOperand2(), programMemory, result, error);
     }
 
+    else if (expr->str() == "[" && expr->astOperand1() && expr->astOperand2()) {
+        if (expr->astOperand1()->values.size() != 1U) {
+            *error = true;
+            return;
+        }
+        const ValueFlow::Value val = expr->astOperand1()->values.front();
+        if (!val.tokvalue || !val.tokvalue->isLiteral()) {
+            *error = true;
+            return;
+        }
+        const std::string strValue = val.tokvalue->strValue();
+        MathLib::bigint index = 0;
+        execute(expr->astOperand2(), programMemory, &index, error);
+        if (index >= 0 && index < (int)strValue.size())
+            *result = strValue[index];
+        else if (index == (int)strValue.size())
+            *result = 0;
+        else
+            *error = true;
+    }
+
     else
         *error = true;
 }

test/testvalueflow.cpp

@@ -1244,6 +1244,14 @@ private:
                "}";
         ASSERT_EQUALS(false, testValueOfX(code, 4U, 0));
 
+        code = "void f() {\n"
+               "    const char abc[] = \"abc\";\n"
+               "    int x;\n"
+               "    for (x = 0; abc[x] != '\\0'; x++) {}\n"
+               "    a[x] = 0;\n"
+               "}";
+        ASSERT_EQUALS(true, testValueOfX(code, 5U, 3));
+
         code = "void f() {\n" // #5939
                "    int x;\n"
                "    for (int x = 0; (x = do_something()) != 0;)\n"