What does the fpermissive flag do

Question

I m just wondering what the -fpermissive flag does in the g   compiler  I am getting      error  taking address of temporary  -fpermissive    which I can solve by giving the  -fpermissive flag to the compiler    EDIT  I just found what was causing the temporary address error part  I m going to fix that part right now

User · Answer

If you want a real-world use case for this, try compiling a very old version of X Windows-- say, either XFree86 or XOrg from aboout 2004, right around the split-- using a "modern" (cough) version of gcc, such as 4.9.3.

You'll notice the build CFLAGS specify both "-ansi" and "-pedantic". In theory, this means, "blow up if anything even slightly violates the language spec". In practice, the 3.x series of gcc didn't catch very much of that kind of stuff, and building it with 4.9.3 will leave a smoking hole in the ground unless you set CFLAGS and BOOTSTRAPCFLAGS to "-fpermissive".

Using that flag, most of those C files will actually build, leaving you free to move on to the version-dependent wreckage the lexer will generate. =]

User · Answer

A common case for simply setting -fpermissive and not sweating it exists  the thoroughly-tested and working third-party library that won t compile on newer compiler versions without -fpermissive   These libraries exist  and are very likely not the application developer s problem to solve  nor in the developer s schedule budget to do it  Set -fpermissive and move on in that case

User · Answer

The -fpermissive flag causes the compiler to report some things that are actually errors  but are permitted by some compilers  as warnings  to permit code to compile even if it doesn t conform to the language rules  You really should fix the underlying problem  Post the smallest  compilable code sample that demonstrates the problem      -fpermissive       Downgrade some diagnostics about nonconformant code from errors to warnings         Thus  using -fpermissive will allow some nonconforming code to compile

User · Answer

When you ve written something that isn t allowed by the language standard  and therefore can t really be well-defined behaviour  which is reason enough to not do it  but happens to map to some kind of executable if fed na  vely to the compiling engine  then -fpermissive will do just that instead of stopping with this error message  In some cases  the program will then behave exactly as you originally intended  but you definitely shouldn t rely on it unless you have some very special reason not to use some other solution

User · Answer

Right from the docs      -fpermissive       Downgrade some diagnostics about nonconformant code from errors to warnings         Thus  using -fpermissive will allow some nonconforming code to compile    Bottom line  don t use it unless you know what you are doing

[c++] What does the fpermissive flag do?

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