问题
I was trying to compile a cpp file: the face-finder in dlib: http://dlib.net/face_detection_ex.cpp.html. But when I ran it, it said I had to include the libraries for jpg and png files:
processing image /home/james/Work/Coding/Sources/Image/950.jpg
exception thrown!
Unable to load image in file /home/dave/Code/Resources/Images/500.jpg.
You must #define DLIB_JPEG_SUPPORT and link to libjpeg to read JPEG files.
Do this by following the instructions at http://dlib.net/compile.html.
Note that you must cause DLIB_JPEG_SUPPORT to be defined for your entire project.
So don't #define it in one file. Instead, use a compiler switch like -DDLIB_JPEG_SUPPORT
so it takes effect for your entire application.
I tried to use the -DDLIB_JPEG_SUPPORT flag, and that failed, so I treid to define them in the file:
*/
#define DLIB_JPEG_SUPPORT
#define DLIB_PNG_SUPPORT
#include </home/james/dlib/image_io.h>
#include </home/james/dlib/image_processing/frontal_face_detector.h>
#include </home/james/dlib/gui_widgets.h>
#include </home/james/dlib/image_io.h>
#include <iostream>
using namespace dlib;
using namespace std;
// ----------------------------------------------------------------------------------------
int main(int argc, char** argv)
but that failed to compile:
james@james-Toshiba-Satellite-8505:~/Work/Coding/Cpp/Dlib/Examples$ g++ -std=c++11 -O3 -I.. ~/dlib/all/source.cpp -lpthread -lX11 face_detection_ex.cpp -o face_detection_ex_2/tmp/ccVHitZj.o: In function `main':
face_detection_ex.cpp:(.text.startup+0x1c0d): undefined reference to `dlib::jpeg_loader::jpeg_loader(std::string const&)'
face_detection_ex.cpp:(.text.startup+0x1d0a): undefined reference to `dlib::jpeg_loader::is_gray() const'
face_detection_ex.cpp:(.text.startup+0x1e3b): undefined reference to `dlib::png_loader::png_loader(std::string const&)'
face_detection_ex.cpp:(.text.startup+0x1f04): undefined reference to `dlib::png_loader::is_gray() const'
face_detection_ex.cpp:(.text.startup+0x1f23): undefined reference to `dlib::png_loader::is_gray() const'
face_detection_ex.cpp:(.text.startup+0x1f38): undefined reference to `dlib::png_loader::is_graya() const'
face_detection_ex.cpp:(.text.startup+0x1f59): undefined reference to `dlib::png_loader::is_graya() const'
face_detection_ex.cpp:(.text.startup+0x1f6e): undefined reference to `dlib::png_loader::is_rgb() const'
face_detection_ex.cpp:(.text.startup+0x1f83): undefined reference to `dlib::png_loader::is_rgb() const'
face_detection_ex.cpp:(.text.startup+0x1f98): undefined reference to `dlib::png_loader::is_rgba() const'
face_detection_ex.cpp:(.text.startup+0x1fad): undefined reference to `dlib::png_loader::is_rgba() const'
face_detection_ex.cpp:(.text.startup+0x2009): undefined reference to `dlib::png_loader::get_row(unsigned int) const'
face_detection_ex.cpp:(.text.startup+0x20b6): undefined reference to `dlib::png_loader::get_row(unsigned int) const'
face_detection_ex.cpp:(.text.startup+0x211c): undefined reference to `dlib::png_loader::~png_loader()'
face_detection_ex.cpp:(.text.startup+0x229a): undefined reference to `dlib::png_loader::get_row(unsigned int) const'
face_detection_ex.cpp:(.text.startup+0x2587): undefined reference to `dlib::png_loader::get_row(unsigned int) const'
face_detection_ex.cpp:(.text.startup+0x2ea7): undefined reference to `dlib::png_loader::~png_loader()'
face_detection_ex.cpp:(.text.startup+0x2fe9): undefined reference to `dlib::png_loader::get_row(unsigned int) const'
face_detection_ex.cpp:(.text.startup+0x30ac): undefined reference to `dlib::png_loader::get_row(unsigned int) const'
face_detection_ex.cpp:(.text.startup+0x313c): undefined reference to `dlib::png_loader::get_row(unsigned int) const'
face_detection_ex.cpp:(.text.startup+0x31c4): undefined reference to `dlib::png_loader::get_row(unsigned int) const'
collect2: error: ld returned 1 exit status
回答1:
Please before ask a question read the error and suggestion messages that compiler and tools show you.
About:
exception thrown! Unable to load image in file /home/dave/Code/Resources/Images/500.jpg. You must #define DLIB_JPEG_SUPPORT and link to libjpeg to read JPEG files. Do this by following the instructions at http://dlib.net/compile.html.
Install libjpeg, libpng, etc. libraries and use them at compilation time to link the program. Please read the suggested page http://dlib.net/compile.html.
Before compile delete the preprocessor directives from your code if you have several source code files.
#define DLIB_JPEG_SUPPORT
#define DLIB_PNG_SUPPORT
and use the suggested switch compiler: -DDLIB_JPEG_SUPPORT.
Note that you must cause DLIB_JPEG_SUPPORT to be defined for your entire project. So don't #define it in one file. Instead, use a compiler switch like -DDLIB_JPEG_SUPPORT so it takes effect for your entire application.
So, use command like this to compile:
g++ face_detection_ex.cpp -o face_detection_ex_2 -std=c++11 -O3 -I.. ~/dlib/all/source.cpp -lpthread -lX11 -ljpeg -lpng -DDLIB_JPEG_SUPPORT -DDLIB_PNG_SUPPORT
Assuming libraries (libjpeg and libpng) have been already installed.
来源：https://stackoverflow.com/questions/43017973/cant-include-the-jpeg-support-headers-in-a-dlib-cpp-file