How to implement the fwrite function as in C language?

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Imtiaz nabi 2022-4-8

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评论： Imtiaz nabi 2022-4-10

Hi there, I want to know if it is possible to implement the fwrite function same as the C language fwrite.

To further explain my question let's say we have fwrite function in C which writes binary data into a file. The syntax of the function is as follow

fwrite(memory containing the data, number of bytes each item to be written, total number of items to write, destination file)

example

fwrite(iq_buff, 2, 2*2600000, signal.bin)

Now my question is how can we specify the number of bytes to be written during the fwrite function and how much data needs to be written in the file?

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Imtiaz nabi 2022-4-8

在 MATLAB Online 中打开

can you provide me some guidance on MEX to use the C function? I have tried using the following command till now

fid = fopen('gps_sig.bin','ab');
fwrite(fid,'int8');
fclose(fid);

Imtiaz nabi 2022-4-8

@Rik If I want to create a wrapper function to get the exact same output what would I need to do? Can you please provide me with any guidance or reference?

I am stuck in specifying the number of elements and bytes to be written

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Walter Roberson 2022-4-8

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编辑：Walter Roberson 2022-4-8

"I want to know if it is possible to implement the fwrite function same as the C language fwrite."

No, it is not possible in MATLAB.

Your prototype for fwrite is incorrect.

https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/fwrite?view=msvc-170

First parameter is the memory location to copy out. In MATLAB that would be the name of the variable, or an expression whose value was to be written out.

Second parameter is the size of one item. In MATLAB that could be the number of bytes in the variable, as determined using whos()

Third parameter is the count. In MATLAB that could be 1.

The fourth parameter to C's fwrite is a pointer to a FILE structure. MATLAB does not have FILE structure, and does not offer pointers (in most contexts). Using the name of a file would not be compatible with C.

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Walter Roberson 2022-4-10

在 MATLAB Online 中打开

If you insist.

function status = FWRITE(data, size_per_element, number_of_elements, fp)
   temp = typecast(data, 'uint8');
   if size_per_element * number_of_elements > numel(temp)
       error('Requested to write more data than exists in the input')
   end
   for offset = 1 : size_per_element : number_of_elements * size_per_element
       fwrite(fp, temp(offset:offset+size_per_element-1), 'uint8');
   end
end

But wouldn't it be a lot easier to just

fwrite(fp, data, 'uint16')

or whatever the appropriate data type is?

Specifying a size of 2 and a large count is nearly the least efficient way to fwrite (writing one byte at a time being worse.) It is more efficient to write in multiples of the physical page size (which is typically 4 Kb)

Imtiaz nabi 2022-4-10

Thank you so much Robert, Actually I am working on a GPS simulator and have generated the Intermediate frequency data but when I use the fwrite function, it writes a very little amount of data which is not enough for the tracking and navigation solution extraction. That's why I wanted to implement the exact code as in the C code hoping that I will get the right amount of data.

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