libcurl issue when using D's std.net.curl on Mac - d

I'm trying to get up to speed using libcurl with D on Mac.
I'm using the latest dmd2 compiler (DMD64 D Compiler v2.062).
The following example compiles and works fine on Windows:
import std.net.curl, std.conv, std.stdio;
void main() {
string content = to!string(get("dlang.org"));
writeln(content);
}
When compiling it on Mac I get the following output:
~/src $ dmd dcurl.d
Undefined symbols for architecture x86_64:
"_curl_easy_cleanup", referenced from:
_D3std3net4curl4Curl8shutdownMFZv in libphobos2.a(curl_1522_37c.o)
"_curl_easy_duphandle", referenced from:
_D3std3net4curl4Curl3dupMFZS3std3net4curl4Curl in libphobos2.a(curl_151e_149.o)
"_curl_easy_init", referenced from:
_D3std3net4curl4Curl10initializeMFZv in libphobos2.a(curl_151d_432.o)
"_curl_easy_perform", referenced from:
_D3std3net4curl4Curl7performMFbZi in libphobos2.a(curl_1528_2fb.o)
"_curl_easy_setopt", referenced from:
_D3std3net4curl4Curl3setMFE3etc1c4curl10CurlOptionlZv in libphobos2.a(curl_1525_14c.o)
_D3std3net4curl4Curl3setMFE3etc1c4curl10CurlOptionAxaZv in libphobos2.a(curl_1524_14c.o)
_D3std3net4curl4Curl3setMFE3etc1c4curl10CurlOptionPvZv in libphobos2.a(curl_1526_14c.o)
_D3std3net4curl4Curl5clearMFE3etc1c4curl10CurlOptionZv in libphobos2.a(curl_1527_207.o)
"_curl_easy_strerror", referenced from:
_D3std3net4curl4Curl11errorStringMFiZAya in libphobos2.a(curl_1520_4a1.o)
"_curl_global_cleanup", referenced from:
_D3std3net4curl4Curl19_sharedStaticDtor29FZv in libphobos2.a(curl.o)
"_curl_global_init", referenced from:
_D3std3net4curl4Curl19_sharedStaticCtor28FZv in libphobos2.a(curl.o)
"_curl_slist_append", referenced from:
_D3std3net4curl3FTP3dupMFZS3std3net4curl3FTP in libphobos2.a(curl_1518_ea.o)
_D3std3net4curl3FTP10addCommandMFAxaZv in libphobos2.a(curl_1518_ea.o)
_D3std3net4curl4HTTP3dupMFZS3std3net4curl4HTTP in libphobos2.a(curl_1517_140.o)
_D3std3net4curl4HTTP16addRequestHeaderMFAxaAxaZv in libphobos2.a(curl_1517_140.o)
"_curl_slist_free_all", referenced from:
_D3std3net4curl3FTP4Impl6__dtorMFZv in libphobos2.a(curl_1518_ea.o)
_D3std3net4curl3FTP13clearCommandsMFZv in libphobos2.a(curl_1518_ea.o)
_D3std3net4curl4HTTP4Impl6__dtorMFZv in libphobos2.a(curl_1517_140.o)
_D3std3net4curl4HTTP19clearRequestHeadersMFZv in libphobos2.a(curl_1517_140.o)
ld: symbol(s) not found for architecture x86_64
collect2: ld returned 1 exit status
--- errorlevel 1
Which seems to imply a linking issue.
I have libcurl at:
/usr/lib/libcurl.3.dylib /usr/lib/libcurl.4.dylib /usr/lib/libcurl.dylib
But I'm not even sure whether dmd is trying to use them.
I've done this before with C/C++ (on the same machine using these libraries) so I think it must be a versioning issue or else I need to pass some flags to the compiler.
Any help would be most appreciated.

You need to link against libcurl. It's not linked against by default. So, instead of
dmd dcurl.d
you need to do
dmd -L-lcurl dcurl.d

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Build Error when compiling c++ code which includes MATLAB Engine Library

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Undefined symbols for architecture x86_64:
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"_engOpen", referenced from:
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I don't think I need to put my actual code here since I am assuming this error has to do with compatibility issues not the code itself. If i'm wrong I will edit the post
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clang++ linker undefined symbols for architecture x86_64

$clang++ main.cpp -o out
Got following error, the same error happens when changing to g++. I have tested on some simple simple c++ code, the command works fine. So it the problem in that PNG class file? However, the same files worked on my MacOS before, but suddenly failed today.
Undefined symbols for architecture x86_64:
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"PNG::operator()(unsigned long, unsigned long)", referenced from:
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"PNG::width() const", referenced from:
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"PNG::height() const", referenced from:
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ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
Did you miss providing static/shared to the linker to resolve the linker errors for the methods mentioned? Also note that clang++ is a different compiler compared to g++ and hence need the static/shared libraries compiled prior by the same compiler you are using (clang++).
Try:
clang++ main.cpp -o out -lpng
Here's why: You are not providing the library that contains the implementation of your PNG library (libpng most likely). You need -lpng added to your compiler, so that it links with the relevant library. It may not be exactly -lpng in your particular case, but it's definitely a "missing library". Without knowing exactly what library you are trying to use (you didn't provide some source to "try the fix with").
As pointed out in the comment: you are using some kind of C++ wrapper on top, the above is probably not enough - but without knowing exactly which C++ wrapper on the png functionality you are actually using, it's hard to say what the command-line should look like.
Perhaps this

Undefined symbols for architecture x86_64: linking mistake?

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I have following linking problem:
Undefined symbols for architecture x86_64:
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"colorFeatures::~colorFeatures()", referenced from:
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"tracker::initTracker(_IplImage*, CvRect*, int, int)", referenced from:
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"tracker::showResults(_IplImage*)", referenced from:
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"tracker::tracker()", referenced from:
_main in main-2b4c23.o
"tracker::~tracker()", referenced from:
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ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
Any kind person has ideas about this problem? Thanks in advance
have gsl installed properly
B) pass to g++ a reference to the lib directory where the gsl libraries are located (probably something like /usr/lib or /usr/local/lib, these should both be default locations for the linker to search), and also to where the header files are, and also tell the linker to do the linking.
g++ -o <name of executable> -L/path/to/gsl/libs -I/path/to/headers -lgsl <name of source file>
the -L tells it where to find the libraries (.so files on linux, .dylib on OS X), -I tells it where to find the headers, -l (that's a lower case L) tells it to link to the library, which would be named libgsl.so or libgsl.dylib.
First just try adding the -lgsl flag, then if it can't find libgsl.so (or .dylib), add the -L flag. NOTE: /path/to/gsl/libs and /path/to/headers are not what you should literally put in there, but replace them with the actual paths on your system.

Xcode 6.3 Apple Match-O linker Error with cocos2d v2.1.5 project

I got a problem when I rebuild cocos2d v2.1.5 with architecture x64 in xcode 6.3. please help me fix this.
Undefined symbols for architecture arm64:
"_WebPGetFeaturesInternal", referenced from:
WebPGetFeatures(unsigned char const*, unsigned long, WebPBitstreamFeatures*) in CCImageCommonWebp.o
"_WebPInitDecoderConfigInternal", referenced from:
WebPInitDecoderConfig(WebPDecoderConfig*) in CCImageCommonWebp.o
"_WebPDecode", referenced from:
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"_NEON_Matrix4Mul", referenced from:
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"_AES_decrypt", referenced from:
DataEncrypt::parseXMLData(unsigned long, char const*) in UserDataEncrypt.o
"_AES_set_encrypt_key", referenced from:
DataEncrypt::save() in UserDataEncrypt.o
"_AES_encrypt", referenced from:
DataEncrypt::save() in UserDataEncrypt.o
"_AES_set_decrypt_key", referenced from:
DataEncrypt::parseXMLData(unsigned long, char const*) in UserDataEncrypt.o
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
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Link to tutorial
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libFLAC symbols not found and vtable errors

I have compiled libFLAC from source code under macintosh os x 10.6.8 and tested WAV to FLAC conversion with success (from the command line). I have also used the default build as such: ./configure --prefix="$base/flac/more/" --exec-prefix="$base/flac/main/" --disable-asm-optimizations && make && make install
Now after adding the paths for FLAC headers and the libs into a brand new project. I am attempting to decode and load FLAC audio into system memory using libFLAC, under the example code which was bundled with libFLAC. However i am getting symbols not found errors with Standard C and vtable symbols not found errors with the Standard C++ approach (as seen below).
Errors under the C approach:
"FLAC_stream_decoder_get_state", referenced from:
_main in main.o
"FLAC_stream_decoder_new", referenced from:
_main in main.o
"FLAC_StreamDecoderStateString", referenced from:
_main in main.o
"FLAC_StreamDecoderErrorStatusString", referenced from:
error_callback(FLAC__StreamDecoder const*,
FLAC__StreamDecoderErrorStatus, void*)in main.o
"FLAC_stream_decoder_init_file", referenced from:
_main in main.o
"FLAC_StreamDecoderInitStatusString", referenced from:
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"FLAC_stream_decoder_set_md5_checking", referenced from:
_main in main.o
"FLAC_stream_decoder_process_until_end_of_stream", referenced from:
_main in main.o
"FLAC_stream_decoder_delete", referenced from:
_main in main.o
ld: symbol(s) not found
collect2: ld returned 1 exit status
From what i can understand is either: the linker is not seeing the libs (because it is seeing the headers) or the libFLAC was not compiled correctly. I'll be thankful if anyone will point me to possible solutions given these errors.
I was doing the linking incorrectly. Linking needs to be done according to this stackoverflow post Adding static library inside Xcode C++ project (How to add static libraries inside a C++ project with Xcode) but i was adding the linking directory under the Project Setting where i was adding my headers path, thus it was not working.