Wrong Values of Doubles from .mat file in C

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Tony Whittam
Tony Whittam 2023-3-28
回答： Tony Whittam 2023-3-29
I have a C program reading a .mat file. The file contains 2 1d arrays of doubles. The program gets a pointer to the beginning of an array of doubles by using mxGetDoubles(). It can successfully read all the values, however there appears to be a scaling problem when printing them with printf("%lf\n", ...) , e.g.
13.69798 displays as as 24.553575
48.94982 displays as as 57.016571
Matlab is R2022a
GCC is x86_64 V11.3.0 (MINGW running in Windows)
Could there be a difference in encoding? I thought they would both use IEEE 754 double encoding.
  2 个评论
Walter Roberson
Walter Roberson 2023-3-28
?? mxGetDoubles() is not (in itself) suitable for reading doubles from a .mat file.
Have you tested with https://www.mathworks.com/help/matlab/matlab_external/reading-a-mat-file-in-cc.html ?
Tony Whittam
Tony Whittam 2023-3-29
编辑：Tony Whittam 2023-3-29
Perhaps I should have given more detail. Here is the C code ...
const char *file1 = "matlab/test/testData/testfile.mat";
MATFile *pmat;
mxArray* pa;
mxArray* pa1;
mxDouble* extData;
pmat = matOpen(file1, "r");
pa1 = matGetNextVariableInfo(pmat, &name);
pa = matGetVariable(pmat, name);
extData = mxGetDoubles(pa);
for (i=0; i<32; i++)
{
printf("%lf\n", extData[i]);
}

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回答（1 个）

Tony Whittam
Tony Whittam 2023-3-29
I just solved our problem. Operator error as usual. We were looking at different data files in Matlab and the C code. Once I opened the same file in Matlab, the numbers were identical to those printed in C.

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