fix err fileExt evoke panic

[cnjack]

No description provided.

[cnjack]

a better idea:(imgcodecs.go)

func IMEncode(fileExt FileExt, img Mat) (buf []byte, err error) {
	cfileExt := C.CString(string(fileExt))
	defer C.free(unsafe.Pointer(cfileExt))

	b := C.Image_IMEncode(cfileExt, img.Ptr())
	defer C.ByteArray_Release(b)
	if b.length == 0 {
		return nil, errors.New("encoder not found")
	}
	return toGoBytes(b), nil
}

[deadprogram]

Hello @cnjack looks like the Windows version of the test you added failed:
https://ci.appveyor.com/project/deadprogram/gocv/build/216#L141

Perhaps it is more sensitive about the extension syntax .jpg?

[cnjack]

catch(...)is not work in mingw?
I found something in https://stackoverflow.com/questions/29271714/catch-across-shared-library-boundary-on-gcc-mingw

[deadprogram]

That figures... well options are to remove the try/catch entirely, or add some conditional platform specific code in the C++. What do you think?

[deadprogram]

The Appveyor build appears to be using shared libs

-DBUILD_SHARED_LIBS=ON here:

https://github.com/hybridgroup/gocv/blob/master/appveyor_build_opencv.cmd#L13

[codecov-io]

Codecov Report

Merging #55 into dev will decrease coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##              dev      #55      +/-   ##
==========================================
- Coverage   96.93%   96.91%   -0.03%     
==========================================
  Files          12       12              
  Lines         913      907       -6     
==========================================
- Hits          885      879       -6     
  Misses         28       28

Impacted Files	Coverage Δ
imgcodecs.go	100% <100%> (ø)	⬆️
dnn.go	100% <0%> (ø)	⬆️
core.go	100% <0%> (ø)	⬆️
highgui.go	75.51% <0%> (ø)	⬆️

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[cnjack]

maybe mingw can not use try-catch?

[deadprogram]

I just commented here on this Go issue, seems like applies to this PR: golang/go#13672 (comment)

[cnjack]

get it, may be it's ok in go1.10

[deadprogram]

Hi @cnjack I do not think this will be fixed anytime soon in Go itself, from all the comments on those issues. However, thanks to replies from @ianlancetaylor a possible solution might be to simply not perform any operations that result in memory allocations taking place in the try/catch block. E.g. something like this:

struct ByteArray Image_IMEncode(const char* fileExt, Mat img) {
    std::vector<uchar> data;
    try{
        cv::imencode(fileExt, *img, data);
        return toByteArray(reinterpret_cast<const char*>(&data[0]), data.size());
    } catch(...) {
        // do not allocate memory here, just pass thru...
    }
    // the following line should only be reached in the case that an exception was encountered...
    return toByteArray(NULL, 0);
}

That might not be best way to structure the code, but it illustrates a technique that might work. Worth a try, I think.

[cnjack]

I will try soon

[cnjack]

sadly, it's not work

[deadprogram]

Oh well. At least we tried that, thanks for making the effort.

[cnjack]

is ok, wait the go fix the problem, the last pr #54 may avoid problems such as these