start to write for a specified location using fprintf

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sermet OGUTCU
sermet OGUTCU 2021-7-12
评论： sermet OGUTCU 2021-7-13
FileName1='data_file';
result_1=23.9;
FileName2='data_file2';
result_2=21.9;
startingFolder='C:\Program Files\MATLAB';
if ~exist(startingFolder, 'dir')
startingFolder = pwd;
end
defaultFileName=fullfile(startingFolder, '*.txt');
[baseFileName, folder]=uiputfile(defaultFileName, 'Select a file');
if baseFileName == 0
return
end
fullFileName = fullfile(folder, baseFileName); %fullfile=building file
fid = fopen(fullFileName, 'w');
How can I write a text file (starting with line 2) for the results as following:
result_1 result_2
data_file: 23.9 data_file2: 21.9

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采纳的回答

Scott MacKenzie
Scott MacKenzie 2021-7-12
Here's a solution. Make sure you use "r+" when opening the file, otherwise you'll overwrite the first line.
fid = fopen('testdata.txt', 'r+'); % open file for reading and writing
fgetl(fid); % skip over 1st line
fprintf(fid','data_file: %.1f data_file2: %.1f\n', result_1, result_2);
fclose(fid);
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Walter Roberson
Walter Roberson 2021-7-12
@Scott MacKenzie
When you switch between reading (fgetl() in this case) and writing (fprintf() in this case), it is necessary to perform an fseek() operation to inform the operating system to flush buffers. It is acceptable to fseek() by 0 bytes relative to the current position: you do not have to move the current position, just call fseek() to prepare for the switch.
fid = fopen('testdata.txt', 'r+'); % open file for reading and writing
fgetl(fid); % skip over 1st line
fseek(fid, 0, 'cof'); %prepare to switch from read to write
fprintf(fid','data_file: %.1f data_file2: %.1f\n', result_1, result_2);
fclose(fid);

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更多回答（1 个）

Scott MacKenzie
Scott MacKenzie 2021-7-12
fid = fopen('testdata.txt', 'w'); % change, as needed
fprintf(fid, ' result_1 result_2\n');
fprintf(fid','data_file: %.1f data_file2: %.1f\n', result_1, result_2);
fclose(fid);
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Scott MacKenzie
Scott MacKenzie 2021-7-12
@Walter Roberson Thanks for pointing this out. Is this documented anywhere? I don't see any mention of this in the fseek documentation.
Walter Roberson
Walter Roberson 2021-7-12
POSIX requirement.
https://pubs.opengroup.org/onlinepubs/9699919799/functions/fseek.html
https://pubs.opengroup.org/onlinepubs/007904975/functions/fopen.html
When a file is opened with update mode ( '+' as the second or third character in the mode argument), both input and output may be performed on the associated stream. However, the application shall ensure that output is not directly followed by input without an intervening call to fflush() or to a file positioning function ( fseek(), fsetpos(), or rewind()), and input is not directly followed by output without an intervening call to a file positioning function, unless the input operation encounters end-of-file.

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