C++11: Invalid Suffix on Literal Warning/Error

I recently came across this unexpected error when compiling C++ code using Clang:

error: invalid suffix on literal; C++11 requires a space between literal and identifier

I got a similar message, although as a warning, when compiling the same code with GCC:

warning: invalid suffix on literal; C++11 requires a space between literal and string macro

The problem occurs when compiling code like this:

printf("Test %"PRIu32"\n", x);

Note that there is no space between the string Test % and PRIu32 which is apparently a requirement in C++11 (or newer). Fortunately, the fix is quite simple – just add spaces between the string and identifier. So the equivalent code below fixes the problem:

printf("Test %" PRIu32 "\n", x);

But what if you have a lot of legacy code that you cannot modify? There are a couple of flags that can disable the warnings/errors, but these are different for Clang and GCC.

NOTE: An obvious way to get rid of the problem in both Clang and GCC is to indicate a C++ standard version earlier than C++11. For example, invoking the compiler with the flag -std=c++03 fixes the problem, but of course, this is not an ideal solution.

Clang

In Clang, the invalid suffix literal message shows as an error by default. You can turn it into a warning message with the -Wno-error=reserved-user-defined-literal flag. Alternatively, you can completely eliminate the warning/error message with -Wno-reserved-user-defined-literal. For example,

clang++ -std=c++11 -Wno-error=reserved-user-defined-literal -c -o test.o test.cpp

NOTE: This page from the Clang documentation explains how the warning and error flags work.

GCC

In GCC, the invalid suffix literal message shows as a warning by default. You can eliminate the message with the Wno-literal-suffix flag. For example,

g++ -std=c++11 -Wno-literal-suffix -c -o test.o test.cpp

NOTE: This page from the GCC documentation explains how the warning and error flags work.