Issue with code to convert C char** to Go []string

[xlab]

Issue with code to convert C char** to Go []string

[xlab]

Oh, there is nothing that can help with guessing the length of the returning array, and as you know there is no Go analog for for (; *shaper_list; shaper_list++) and never will be one. With plain types that are stored contiguously in memory like []float32 a pack method just creates a slice-view with quite large cap, the length can be later set by user with slicing.

As for this case, that's an array of complex types and they need to be packed one-by-one, and only you know the limit. So, the only option here is to actually copy that snippet generated by cgogen into a separate file and complete it, like that:

// BufferGetGlyphInfos function as declared in harfbuzz/hb-buffer.h:372
func BufferGetGlyphInfos(buffer *Buffer, length *uint32) []GlyphInfo {
    cbuffer, _ := (*C.hb_buffer_t)(unsafe.Pointer(buffer)), cgoAllocsUnknown
    clength, _ := (*C.uint)(unsafe.Pointer(length)), cgoAllocsUnknown
    __ret := C.hb_buffer_get_glyph_infos(cbuffer, clength)
    var __v = make([]GlyphInfo, *length)
    packSGlyphInfo(__v, __ret)
    return __v
}

Voilá! An exercise to the reader: make the original method private, so it won't cause a name collision while still triggering the required helper func generation (like packSGlyphInfo).

[deepakjois]

This seems to be occuring in other places as well. Here is another example of a nil slice being sent to the packing function (which will effectively return an empty slice as a return value):

// BufferGetGlyphInfos function as declared in harfbuzz/hb-buffer.h:372
func BufferGetGlyphInfos(buffer *Buffer, length *uint32) []GlyphInfo {
    cbuffer, _ := (*C.hb_buffer_t)(unsafe.Pointer(buffer)), cgoAllocsUnknown
    clength, _ := (*C.uint)(unsafe.Pointer(length)), cgoAllocsUnknown
    __ret := C.hb_buffer_get_glyph_infos(cbuffer, clength)
    var __v []GlyphInfo
    packSGlyphInfo(__v, __ret)
    return __v
}