Require the result of StringPrintf to be used.

base/strings/stringprintf.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_STRINGS_STRINGPRINTF_H_
 #define BASE_STRINGS_STRINGPRINTF_H_
 
 #include <stdarg.h>   // va_list
 
 #include <string>
 
 #include "base/base_export.h"
 #include "base/compiler_specific.h"
 
 namespace base {
 
 // Return a C++ string given printf-like input.
 BASE_EXPORT std::string StringPrintf(const char* format, ...)
-    PRINTF_FORMAT(1, 2);
+    PRINTF_FORMAT(1, 2) WARN_UNUSED_RESULT;
 // OS_ANDROID's libc does not support wchar_t, so several overloads are omitted.
 #if !defined(OS_ANDROID)
 BASE_EXPORT std::wstring StringPrintf(const wchar_t* format, ...)
-    WPRINTF_FORMAT(1, 2);
+    WPRINTF_FORMAT(1, 2) WARN_UNUSED_RESULT;
 #endif
 
 // Return a C++ string given vprintf-like input.
 BASE_EXPORT std::string StringPrintV(const char* format, va_list ap)
-    PRINTF_FORMAT(1, 0);
+    PRINTF_FORMAT(1, 0) WARN_UNUSED_RESULT;
 
 // Store result into a supplied string and return it.
 BASE_EXPORT const std::string& SStringPrintf(std::string* dst,
                                              const char* format, ...)
     PRINTF_FORMAT(2, 3);
 #if !defined(OS_ANDROID)
 BASE_EXPORT const std::wstring& SStringPrintf(std::wstring* dst,
                                               const wchar_t* format, ...)
     WPRINTF_FORMAT(2, 3);
 #endif
@@ skipping 14 matching lines @@
     PRINTF_FORMAT(2, 0);
 #if !defined(OS_ANDROID)
 BASE_EXPORT void StringAppendV(std::wstring* dst,
                                const wchar_t* format, va_list ap)
     WPRINTF_FORMAT(2, 0);
 #endif
 
 }  // namespace base
 
 #endif  // BASE_STRINGS_STRINGPRINTF_H_