Julia系列14：调用自定义C/C++库

1. 基础调用：ccall

调用的基本格式为：
ccall((:函数名, 库地址), 输出格式, (输入格式列表), 输入数据)

下面是例子：

1.1 基础数据结构

1.2 数组

首先是输入数组，注意需要convert

接着是输出数组，需要使用unsafe_wrap进行转换，并且需要用GC.@perserve防止垃圾回收

二维数组需要在C中注意编号

1.3 字符串

1.4 复杂数据结构

2. AST分析：Clang.jl

假设我们有一个头文件：

// example.h
struct ExStruct {
    int    kind;
    char*  name;
    float* data;
};

void* ExFunction (int kind, char* name, float* data) {
    struct ExStruct st;
    st.kind = kind;
    st.name = name;
    st.data = data;
}

使用julia查看和分析头文件的代码为：

julia> using Clang

julia> trans_unit = Clang.parse_header(Index(), "example.h")
TranslationUnit(Ptr{Nothing} @0x00007fe13cdc8a00, Index(Ptr{Nothing} @0x00007fe13cc8dde0, 0, 1))

julia> root_cursor = Clang.getTranslationUnitCursor(trans_unit)
CLCursor (CLTranslationUnit) example.h

julia> struct_cursor = search(root_cursor, "ExStruct") |> only
CLCursor (CLStructDecl) ExStruct

julia> for c in children(struct_cursor)  # print children
           println("Cursor: ", c, "\n  Kind: ", kind(c), "\n  Name: ", name(c), "\n  Type: ", Clang.getCursorType(c))
       end
Cursor: CLCursor (CLFieldDecl) kind
  Kind: CXCursor_FieldDecl(6)
  Name: kind
  Type: CLType (CLInt)
Cursor: CLCursor (CLFieldDecl) name
  Kind: CXCursor_FieldDecl(6)
  Name: name
  Type: CLType (CLPointer)
Cursor: CLCursor (CLFieldDecl) data
  Kind: CXCursor_FieldDecl(6)
  Name: data
  Type: CLType (CLPointer)

TranslationUnit是AST的入口，包含3部分内容：
Kind: purpose of cursor node
Type: type of the object represented by cursor
Children: list of child nodes

Clang.getTranslationUnitCursor方法可以获得其根节点。

接下来是获取方法详情：

julia> using Clang.LibClang  # CXCursor_FunctionDecl is exposed from LibClang

julia> fdecl = search(root_cursor, CXCursor_FunctionDecl) |> only
CLCursor (CLFunctionDecl) ExFunction(int, char *, float *)

julia> fdecl_children = [c for c in children(fdecl)]
4-element Array{CLCursor,1}:
 CLCursor (CLParmDecl) kind
 CLCursor (CLParmDecl) name
 CLCursor (CLParmDecl) data
 CLCursor (CLCompoundStmt)

julia> [Clang.getCursorType(t) for t in fdecl_children[1:3]]
3-element Array{CLType,1}:
 CLType (CLInt)     
 CLType (CLPointer)
 CLType (CLPointer)

julia> [Clang.getPointeeType(Clang.getCursorType(t)) for t in fdecl_children[2:3]]
2-element Array{CLType,1}:
 CLType (CLChar_S)
 CLType (CLFloat)