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open file, read a line then, rewind a line

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Sam
Sam 2012-11-30
after fgetl(fid), the file position indicatior will be moved to the next line in the file, how could I rewind the indicator back 1 line in the file so when I call fgetl(fid) the second time it would return the same line?
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Sam
Sam 2012-11-30
say this is the text file i want to read
my line 1
my line 2
my line 3
my line 4
say after some steps, fgetl(fid) would return 'my line 3', then what should I do so when I call fgetl(fid) after this, it would still return 'my line 3'?

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回答（1 个）

Matt J
Matt J 2012-11-30
编辑：Matt J 2012-11-30
Use FTELL to measure the position in bytes of each line. Then use FREWIND and/or FSEEK to go to the desired position.
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Walter Roberson
Walter Roberson 2012-11-30
Technical note:
If a file is opened with 'rt', which should be used for text files, then the value returned by ftell() is an arbitrary "token" rather than a file offset in bytes. Using the same token will get you to the same position, but you cannot do computations on the tokens.

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