Fix #14743 (New check: ftell() result is unspecified when file is opened in mode "t")

.gitignore

@@ -2,6 +2,7 @@
 *.gcno
 *.gch
 *.o
+*.a
 *.pyc
 /cppcheck
 /cppcheck.exe

lib/checkio.cpp

@@ -48,6 +48,7 @@
 // CVE ID used:
 static const CWE CWE119(119U);  // Improper Restriction of Operations within the Bounds of a Memory Buffer
 static const CWE CWE398(398U);  // Indicator of Poor Code Quality
+static const CWE CWE474(474U);  // Use of Function with Inconsistent Implementations
 static const CWE CWE664(664U);  // Improper Control of a Resource Through its Lifetime
 static const CWE CWE685(685U);  // Function Call With Incorrect Number of Arguments
 static const CWE CWE686(686U);  // Function Call With Incorrect Argument Type
@@ -111,6 +112,8 @@ namespace {
         nonneg int op_indent{};
         enum class AppendMode : std::uint8_t { UNKNOWN_AM, APPEND, APPEND_EX };
         AppendMode append_mode = AppendMode::UNKNOWN_AM;
+        enum class ReadMode : std::uint8_t { READ_TEXT, READ_BIN };
+        ReadMode read_mode = ReadMode::READ_BIN;
         std::string filename;
         explicit Filepointer(OpenMode mode_ = OpenMode::UNKNOWN_OM)
             : mode(mode_) {}
@@ -183,6 +186,7 @@ void CheckIOImpl::checkFileUsage()
                 }
             } else if (Token::Match(tok, "%name% (") && tok->previous() && (!tok->previous()->isName() || Token::Match(tok->previous(), "return|throw"))) {
                 std::string mode;
+                bool isftell = false;
                 const Token* fileTok = nullptr;
                 const Token* fileNameTok = nullptr;
                 Filepointer::Operation operation = Filepointer::Operation::NONE;
@@ -266,6 +270,9 @@ void CheckIOImpl::checkFileUsage()
                     fileTok = tok->tokAt(2);
                     if ((tok->str() == "ungetc" || tok->str() == "ungetwc") && fileTok)
                         fileTok = fileTok->nextArgument();
+                    else if (tok->str() == "ftell") {
+                        isftell = true;
+                    }
                     operation = Filepointer::Operation::UNIMPORTANT;
                 } else if (!Token::Match(tok, "if|for|while|catch|switch") && !mSettings.library.isFunctionConst(tok->str(), true)) {
                     const Token* const end2 = tok->linkAt(1);
@@ -321,10 +328,15 @@ void CheckIOImpl::checkFileUsage()
                             f.append_mode = Filepointer::AppendMode::APPEND_EX;
                         else
                             f.append_mode = Filepointer::AppendMode::APPEND;
+                    }
+                    else if (mode.find('r') != std::string::npos &&
+                             mode.find('t') != std::string::npos) {
+                        f.read_mode = Filepointer::ReadMode::READ_TEXT;
                     } else
                         f.append_mode = Filepointer::AppendMode::UNKNOWN_AM;
                     f.mode_indent = indent;
                     break;
+
                 case Filepointer::Operation::POSITIONING:
                     if (f.mode == OpenMode::CLOSED)
                         useClosedFileError(tok);
@@ -357,6 +369,8 @@ void CheckIOImpl::checkFileUsage()
                 case Filepointer::Operation::UNIMPORTANT:
                     if (f.mode == OpenMode::CLOSED)
                         useClosedFileError(tok);
+                    if (isftell && f.read_mode == Filepointer::ReadMode::READ_TEXT && printPortability)
+                        ftellFileError(tok);
                     break;
                 case Filepointer::Operation::UNKNOWN_OP:
                     f.mode = OpenMode::UNKNOWN_OM;

lib/checkio.h

@@ -127,6 +127,7 @@ class CPPCHECKLIB CheckIOImpl : public CheckImpl {
     void useClosedFileError(const Token *tok);
     void fcloseInLoopConditionError(const Token *tok, const std::string &varname);
     void seekOnAppendedFileError(const Token *tok);
+    void ftellFileError(const Token *tok);
     void incompatibleFileOpenError(const Token *tok, const std::string &filename);
     void invalidScanfError(const Token *tok);
     void wrongPrintfScanfArgumentsError(const Token* tok,

man/checkers/ftellTextModeFile.md

@@ -0,0 +1,56 @@
+# ftellModeTextFile
+
+**Message**: ftell() result is unspecified when file is opened in mode "t".<br/>
+**Category**: Portability<br/>
+**Severity**: Style<br/>
+**Language**: C/C++
+
+## Description
+
+This checker detects the use of ftell() on a file open in text (or translate) mode. The text mode is not consistent
+ in between Linux and Windows system and may cause ftell() to return the wrong offset inside a text file.
+
+See section 7.21.9.4p2 of the C11 standard regarding the ftell function states for a text stream:
+
+- For a text stream, its file position indicator contains unspecified information, usable by the fseek function for returning the file position indicator for the stream to its position at the time of the ftell call; the difference between two such return values is not necessarily a meaningful measure of the number of characters written or read.
+
+This warning helps improve code quality by:
+- Making the intent clear that the use of ftell() in "t" mode may cause portability problem.
+
+## Motivation
+
+This checker improves portability accross system.
+
+## How to fix
+
+According to C11, the file must be opened in binary mode 'b' to prevent this problem.
+
+Before:
+```cpp
+     FILE *f = fopen("Example.txt", "rt");
+     if (f)
+     {
+        fseek(f, 0, SEEK_END);
+        printf( "File size %d\n", ftell(f));
+        fclose(f);
+     }
+
+```
+
+After:
+```cpp
+
+     FILE *f = fopen("Example.txt", "rb");
+     if (f)
+     {
+        fseek(f, 0, SEEK_END);
+        printf( "File size %d\n", ftell(f));
+        fclose(f);
+     }
+
+```
+
+## Notes
+
+See https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/fopen-wfopen?view=msvc-170
+

releasenotes.txt

@@ -9,6 +9,7 @@ New checks:
 - funcArgNamesDifferentUnnamed warns on function declarations/definitions where a parameter in either location is unnamed
 - uninitMemberVarNoCtor warns on user-defined types where (1) some but not all members requiring initialization have in-class initializers or (2) there is a mixture of members which do/do not require initialization.
 - fcloseInLoopCondition warns when fclose() is used as a while loop condition, which may skip the loop body or double-close the file handle.
+- ftell() result is unspecified when file is opened in mode "t".
 
 C/C++ support:
 -

test/testio.cpp

@@ -44,6 +44,7 @@ class TestIO : public TestFixture {
         TEST_CASE(fileIOwithoutPositioning);
         TEST_CASE(seekOnAppendedFile);
         TEST_CASE(fflushOnInputStream);
+        TEST_CASE(ftellCompatibility);
         TEST_CASE(incompatibleFileOpen);
 
         TEST_CASE(testScanf1); // Scanf without field limiters
@@ -727,6 +728,22 @@ class TestIO : public TestFixture {
         ASSERT_EQUALS("", errout_str()); // #6566
     }
 
+    void ftellCompatibility() {
+
+        check("void foo() {\n"
+              "     FILE *f = fopen(\"\", \"rt\");\n"
+              "     if (f)\n"
+              "     {\n"
+              "         extern long position;\n"
+              "         fseek(f, 0, SEEK_END);\n"
+              "         position = ftell(f);\n"
+              "         fclose(f);\n"
+              "     }\n"
+              "}\n", dinit(CheckOptions, $.portability = true));
+        ASSERT_EQUALS("[test.cpp:7:21]: (portability) ftell() result is unspecified when file is opened in mode \"t\" [ftellTextModeFile]\n", errout_str());
+    }
+
+
     void fflushOnInputStream() {
         check("void foo()\n"
               "{\n"