how to compile fftw3 on iOS - c++

Question

Nowdays I just want to use FFTW3 on iOS, since I've compiled it successfully into i386 version which is used by the iOS simulator, the rest work is to compile it into armv6(or v7) version and lipo these two versions together,below is my incorrect configure:
./configure
CC=/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/arm-apple-darwin10-gcc-4.2.1
LD=/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/ld
CCFLAGS="-I
/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.2.sdk/usr/lib/gcc/arm-apple-darwin10/4.2.1/include/
-I /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.2.sdk/usr/include/
-miphoneos-version-min=2.2 -arch armv6 -isysroot /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.2.sdk"
LDFLAGS="-arch armv6 -isysroot
/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.2.sdk"
--enable-float --host=arm-apple-darwin --build=arm-apple-darwin10 --disable-fortran
when use this to build fftw3,I always get this:
checking for a BSD-compatible install... /usr/bin/install -c
checking whether build environment is sane... yes
checking for arm-apple-darwin-strip... no
checking for strip... strip
configure: WARNING: using cross tools not prefixed with host triplet
checking for a thread-safe mkdir -p... ./install-sh -c -d
checking for gawk... no
checking for mawk... no
checking for nawk... no
checking for awk... awk
checking whether make sets $(MAKE)... yes
checking whether to enable maintainer-specific portions of Makefiles... no
checking build system type... arm-apple-darwin10
checking host system type... arm-apple-darwin
checking for arm-apple-darwin-gcc... /Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/arm-apple-darwin10-gcc-4.2.1
checking whether the C compiler works... no
configure: error: in /Users/chencyz/Desktop/Development/Misc/fftw3/fftw-3.3':
configure: error: C compiler cannot create executables
Seeconfig.log' for more details
I'm not so clear about the problem(C compiler not works?),could anyone give me some guides,thanks very much !

Answer 1

According to ./configure --help:
--build=BUILD configure for building on BUILD [guessed]
--host=HOST cross-compile to build programs to run on HOST [BUILD]
So the key is to pass --host=arm-apple-darwin10, and execute configure with the correct alterations to PATH, CFLAGS, LDFLAGS, etc.
This seems to work:
PATH=/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin:$PATH \
../configure --host=arm-apple-darwin10 CFLAGS="-I/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.3.sdk/usr/include -I/Library/iPhone/include -isysroot /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.3.sdk" \
CC=arm-apple-darwin10-gcc-4.2.1 \
CPP=cpp \
LDFLAGS="-isysroot /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.3.sdk" \
--enable-single
Good luck.

Answer 2

I had a similar issue when trying to get cute compiled for iOS. Looking at the configure script, it didn't seem to use the $LDFLAGS variable, but if it did I think you could add the following to the configure line:
./configure CC=... CFLAGS="-arch armv7 -isysroot $SDKROOT" CXXFLAGS="$CFLAGS" LDFLAGS="$CFLAGS -Wl,-syslibroot $SDKROOT"
Where $SDKROOT is /Developer/Platforms/iPhone.platform/Developer/SDKs/iPhone5.0.sdk by default (with the iOS 5.0 SDK).
I never got cute compiled as I couldn't figure out how to correct the C-compiler invocation, however, your mileage may vary.