I need to compile a code written in C using gcc (in Xcode) with flag options -ansi -pedantic. I know how to change the compiler to gcc, however I don't know how to change the flags.
Thanks in advance.
Use the Other C Flags build setting to add compiler flags that aren't available in Xcode's build settings editor.
Related
With IBM's cc compiler there is one option -brtl.
cc-brtl .....
This option does the following:-
-brtl Tells the linkage editor to accept both .so and .a library file types.
I am using gcc compiler now on ubuntu. I want to know what is the corresponding option in gcc to achieve
the same thing?
You don't need that option for gcc. The link editor will accept both so and a files by default, with so files being preferred. You can think of gcc as having the opposite behaviour to IBM's C compiler: The behaviour without any options is as if you provided -brtl to IBM's C compiler, while the option -static turns of dynamic linking (and thus causes gcc to not take so files into consideration), which is as if you didn't specify -brtl to IBM's C compiler.
I have a automake enabled project which I would like to compile with clang. I have added a configure option to enable clang:
AC_ARG_ENABLE([clang],
[AS_HELP_STRING([--enable-clang],[use clang instead of gcc as C compiler.])])
#Use C99 compilation mode
if test "x$enable_clang" = "xyes"; then
# clang uses c99 mode by default, so we just set CC to clang and we are done
CC="clang";
else
# We do not need to set CC as the default is gcc, but we need to set it to
# use C99 compilation mode
CFLAGS="$CFLAGS -std=c99";
fi
Further up in the file I have also the following two macros, to enable gettext functionality:
AM_GNU_GETTEXT_VERSION([0.18.1])
AM_GNU_GETTEXT([external])
If these two macros are present then configure ignores that the CC variable is set to clang and falls back to gcc. I have to comment out the gettext macros and then clang is used.
Obviously there is some problem with GETTEXT and clang. Am I using the wrong macro, or is clang not able to use the gnu gettext library? How can I fix this?
Have you tried to set CC to clang before you check for libraries (like gettext)? – Some programmer dude
Nice that worked. – lanoxx
I've created a Plain C project in Qt Creator in Linux, but I'm getting this error:
error: 'for' loop initial declarations are only allowed in C99 mode
note: use option -std=c99 or -std=gnu99 to compile your code
What should I put in my *.pro file to enable C99?
QMAKE_CFLAGS += -std=c99
This worked for me, even though it is not documented and the intellisense doesn't recognize it.
You could set QMAKE_CC or QMAKE_CFLAGS_DEBUG and QMAKE_CFLAGS_RELEASE to contain -std=c99, e.g. add into your .pro file
QMAKE_CC= gcc -std=c99
I've recently learned how to program simple character drivers and while playing around with the code I noticed that I get a lot of the following GCC warnings thrown for my C99 code:
warning: ISO C90 forbids mixed declarations and code
I assume this is because the main Linux kernel Makefile is set to compile using a non-C99 standard. I searched around I found this answer here on stackoverflow: How to use make and compile as C99?
So I naturally tried the following in my Makefile:
ccflags-y := -std=gnu99
Unfortunately this didn't silence the GCC warnings. I checked the verbose output of make and verified that GCC is indeed executed with the -std=gnu99 tacked on at the end; so I'm a bit confused.
How do I properly compile a Linux kernel module using the -std=gnu99 option?
EDIT:
I noticed the GCC output shows this option: -Wdeclaration-after-statement. Is this why I am getting the warnings even with the -std=gnu99 option?
It turns out that -std=gnu99 does in fact work; I began seeing errors regarding C99 features after removing the compiler flag. So that meant something else was causing the warnings to print out besides the -std= option.
After parsing through the verbose output via make V=1, I discovered the -Wdeclaration-after-statement option as part of the GCC execution. This was the cause of the ISO C90 mixed declaration warnings I saw.
To disable the ISO C90 warnings, pass this to GCC: -Wno-declaration-after-statement.
For example:
ccflags-y := -std=gnu99 -Wno-declaration-after-statement
You can also specify the flag in your Makefile, if you have one:
FLAGS=-std=gnu99
I'm writing a shared library using autoconf/libtool which I want to compile for Linux and for Windows (Using the mingw cross-compiler). For Linux (and maybe other platforms which support it) I need to set -fPIC. So I put it into the CFLAGS in Makefile.am. But when I cross-compile it with mingw then gcc complains with a warning:
warning: -fPIC ignored for target (all code is position independent)
So obviously this option is not needed for Windows code. It is only a warning but I want to get rid of it anyway. How can I do this? Maybe there is already a libtool/autoconf feature which checks if the option is supported and only sets it when needed so I don't have to do this manually in Makefile.am?
You shouldn't need to set -fPIC manually, libtool will add it if you tell it what type of binary/library you're building.
lib_LTLIBRARIES = mylibrary.la
mylibrary_la_SOURCES = mylibrary.c
This can produce both a mylibrary.so with PIC (if needed) and a mylibrary.a without, depending on other Autoconf/Automake options. (Probably something like .dll and .lib on Windows, but I don't use that platform.)
I have used the following in configure.ac to add -fPIC conditionally:
AC_MSG_CHECKING(whether fPIC compiler option is accepted)
SAVED_CFLAGS="$CFLAGS"
CFLAGS="$CFLAGS -fPIC -Werror"
AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [return 0;])],
[AC_MSG_RESULT(yes)
CFLAGS="$SAVED_CFLAGS -fPIC"],
[AC_MSG_RESULT(no)
CFLAGS="$SAVED_CFLAGS"])