What does the expression "a+t" mean in the second parameter of fopen in C?

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I was coming across a code here and I was curious about this excerpt: 

FILE *fp = fopen("Agenda.txt","a+t");

What’s the point of "a+t"?

c filing-cabinet fopen

  • Look, the "t" I don’t know, because I don’t know much C. But I can assure you that a means: "always add content from the last line of the file"

  • That’s right, thank you!!

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2 answers

8

This is the access mode to the file being opened. "a+" indicates that you can only add data at the end of the file (append) and that can be read as well ("+"). Recording must always be made official with fflush().

"t" indicates that you can only use text, but this is not standard C. Only some specific compiler accepts on specific platform, but this is considers a undefined behavior.

Documentation.

  • How the file is opened with fopen(), has to be effected using fflush().

  • @Wtrmute yes, I think it was just typo, thank you.

2

According to the website of fopen.

"a+t" or "at+" it opens a text file in read or update mode (adding the new information at the end of the file).

  • Thank you very much!

  • The "text mode" refers to the translation of car returns, which it converts when reading from CR LF for LF, and the opposite when writing. A flag opposite, b, explicitly disables this conversion.

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