“first argument not a pointer or valid constant expression” in ccall, v0.7-alpha

[jonathanBieler]

This seems to be a bug:

module B
    using Cairo

    test() = ccall((:cairo_version_string,Cairo._jl_libcairo),Cstring,()) 
end

julia> B.test()
ERROR: TypeError: in test, in ccall: first argument not a pointer or valid constant expression, expected Ptr, got Tuple{Symbol,String}

[JeffBezanson]

I looked into this; it's due to the fact that we have special evaluation for getfield calls in ccall but not for getproperty.

[cuihantao]

I'm new to Julia, and I ran into a similar issue. The slightly modified code from the op's doesn't work.

Please kindly suggest if I made a mistake. Thank you! @JeffBezanson

      module B
           using Cairo
           lib_path = Cairo._jl_libcairo
           test() = ccall((:cairo_version_string, lib_path),Cstring,())
       end

julia> B.test()
ERROR: TypeError: in ccall: first argument not a pointer or valid constant expression, expected Ptr, got Tuple{Symbol,String}
Stacktrace:
 [1] test() at ./REPL[1]:4
 [2] top-level scope at none:0

[cuihantao]

Running Julia 1.1.0 on darwin64 by the way. I found a workaround:

module B
    using Cairo
    lib_path = Cairo._jl_libcairo
    test() = eval(:(ccall((:cairo_version_string, $lib_path),Cstring,())))
end

julia> B.test()
Cstring(0x000000012c08bc49)

[cuihantao]

I'm trying to parametrize the argument type but ran into another issue. See the sample code below

julia> module B
           using Cairo
           lib_path = Cairo._jl_libcairo
           arg_type = ()
           call_str =:(ccall((:cairo_version_string, $lib_path),Cstring,$arg_type))
           dump(call_str)
           test() = eval(call_str)
       end
WARNING: replacing module B.
Expr
  head: Symbol call
  args: Array{Any}((4,))
    1: Symbol ccall
    2: Expr
      head: Symbol tuple
      args: Array{Any}((2,))
        1: QuoteNode
          value: Symbol cairo_version_string
        2: String "/Users/hcui7/.julia/packages/Homebrew/s09IX/deps/usr/lib/libcairo.dylib"
    3: Symbol Cstring
    4: Tuple{} ()
Main.B

julia> B.test()
ERROR: syntax: ccall argument types must be a tuple; try "(T,)"
Stacktrace:
 [1] eval at ./boot.jl:328 [inlined]
 [2] eval at ./REPL[10]:1 [inlined]
 [3] test() at ./REPL[10]:7
 [4] top-level scope at none:0

But if I hard-code the arg_type like in the last post, it works:

julia> module B
           using Cairo
           lib_path = Cairo._jl_libcairo
           arg_type = ()
           call_str =:(ccall((:cairo_version_string, $lib_path),Cstring,()))
           dump(call_str)
           test() = eval(call_str)
       end
WARNING: replacing module B.
Expr
  head: Symbol call
  args: Array{Any}((4,))
    1: Symbol ccall
    2: Expr
      head: Symbol tuple
      args: Array{Any}((2,))
        1: QuoteNode
          value: Symbol cairo_version_string
        2: String "/Users/hcui7/.julia/packages/Homebrew/s09IX/deps/usr/lib/libcairo.dylib"
    3: Symbol Cstring
    4: Expr
      head: Symbol tuple
      args: Array{Any}((0,))
Main.B

julia> B.test()
Cstring(0x0000000123892c49)

Julia>

[yuyichao]

Please use discourse for questions.

[cuihantao]

Ok, just posted to discourse @yuyichao