First output of calllib is always double.

Question

Zachary Smoot 2024-4-24

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2111471-first-output-of-calllib-is-always-double

回答： Paras Gupta 2024-4-30

采纳的回答： Paras Gupta

在 MATLAB Online 中打开

If I have a function in a C library declared in a C header like so:

long long some_function();

And call the function like so:

loadlibrary('the_library', 'the_header.h');
out = calllib('the_library', 'some_function');

The output "out" is of type double, instead of int64.

When generating a prototype file for the library, the value of "LHS" is detected as "int64", but this does not seem to effect what the actuall output type is when calling the function.

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Paras Gupta 2024-4-30

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2111471-first-output-of-calllib-is-always-double#answer_1450161

Hey Zachary,

In my understanding, you want the output type of the 'calllib()' function to be 'int64' instead of 'double' for a C function with return type "long long".

The type for all scalar values returned by MATLAB is 'double' by default. Please refer to the note given in the following documentation:

https://www.mathworks.com/help/matlab/matlab_external/passing-arguments-to-shared-library-functions.html

To convert the output to 'int64', you can try the following two workarounds:

Using the 'int64()' function on the output - https://www.mathworks.com/help/matlab/ref/int64.html
Modifying the function definition to return an array pointer with type "long long" instead of a scalar output. The 'out' variable in MATLAB will then be a 'libpointer' object - https://www.mathworks.com/help/matlab/ref/libpointer.html

Hope this helps.