How to read and write to global variables of shared library(using loadlibrary)?

Question

Nilendra Gadre 2020-4-1

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/514476-how-to-read-and-write-to-global-variables-of-shared-library-using-loadlibrary

编辑： Mohammad Sami 2020-4-1

采纳的回答： Mohammad Sami

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A C dll contains functions fn1(),fn2() etc which take some input arguments and give some outputs.

The processing and output of the fn1() depends on global varaibles (exported in dll header).

When the dll is loaded using

>> loadlibrary('dllname','dllname.h') 
>> m = libfunctions('dllname', '-full')

Output is:

>> m = 
    'fn1'
    'fn2'
    'lib.pointer globalVar1'
    'lib.pointer globalVar2'
    .
    .

Question is how to modify value of this globalVar1 in matlab?

Ex:

prev_value = globalVar1;
globalVar1 = newValue;
output = calllib('dllname','fn1',arg1);

Similarly, how to modify if the global variables are structures?

Thanks in Advance.

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Answer 1

Mohammad Sami 2020-4-1

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https://ww2.mathworks.cn/matlabcentral/answers/514476-how-to-read-and-write-to-global-variables-of-shared-library-using-loadlibrary#answer_423239

编辑：Mohammad Sami 2020-4-1

在 MATLAB Online 中打开

You need to get the pointer first. Try the following to see if it works.

Also you did not specify what data type the pointer is pointing to in the question.

globalpointer1 = calllib('dllname','globalVar1');
prev_value = globalpointer1.Value;
globalpointer1.Value = int8(2); % assuming a data type and value.
output = calllib('dllname','fn1',arg1);

Structures should be returned as libstruct objects. See the libstruct documentations for details.

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Mohammad Sami 2020-4-1

编辑：Mohammad Sami 2020-4-1

在 MATLAB Online 中打开

try this way.

globalpointer1 = calllib('dllname','globalVar1');
setdatatype(globalpointer1,'int32Ptr',1,1);
prev_value = globalpointer1.Value;
globalpointer1.Value = int32(2); % assuming a data type and value.
% arg1 ....
output = calllib('dllname','fn1',arg1);