How can i read the line above a certain position?

Question

Jiahong Zou 2023-6-26

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1988133-how-can-i-read-the-line-above-a-certain-position

回答： Joe Vinciguerra 2023-6-26

This is how the Nastran file looks like

$$  PSHELL Data           
$
$HMNAME PROP             5101090"PSHELL_5101090" 4
$HWCOLOR PROP            5101090      44
PSHELL   510109096069002VAR0000696069002        96069002                
$INSERT_PSHELL

I want to read the line above $INSERT_PSHELL. So i have ChatGPT part of this code written for me, which didn't work at all

function [PID, IDENT] = addPSHELL(inputDir, fileName, elementList)
%% function add exact many PSHELL properties as elements in element list 
    NumberToAdd = numel(elementList);
    
    % Read the original file
    fid = fopen(fullfile(inputDir, fileName), 'rt');
    if fid == -1
        error('Failed to open the file.');
    end
    
    % Move to the position where identifier is
    while ~feof(fid)
        line = fgetl(fid);
        
        % Check if the line contains the identifier and move
        if contains(line, '$INSERT_PSHELL')
            IdentifierPosition = ftell(fid);
            break;
        end
    end
    % Read the last PSHELL to get PID
    fseek(fid, IdentifierPosition, 'bof');
  
    while ftell(fid) > 0
        fseek(fid, -1, 'cof');  % Move back one byte
        
        % Check if the previous byte is a newline character
        if fread(fid, 1, 'char') == 10
            break;  % Found the line above
        end
        
        fseek(fid, -1, 'cof');  % Move back one more byte
    end
    
    lineAbove = fgetl(fid);
    
    if ~(rem(length(lineAbove), 8) == 0)
        error('the line above is not 8 multiples digit long')
    end
    
    % Break the line into 8-digit pieces
    for i = 1:(length(lineAbove) \ 8)
        lineAbove{i} = lineAbove(1+8*i : 8*i);  % PSHELL PID MID1 T MID2 .....            
    end

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Answer 1

Joe Vinciguerra 2023-6-26

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1988133-how-can-i-read-the-line-above-a-certain-position#answer_1262633

在 MATLAB Online 中打开

Replace "file_name" with whatever the name of your file is:

f = readlines(file_name);  % read the file
k = find(f == "$INSERT_PSHELL");  % find the line number that matches your criteria
result = f(k-1); % this is the text on the line above it