The ungetc() function pushes a character onto an input stream. This pushed character can then be read by subsequent calls to functions that read from that stream. However, the ungetc() function has serious limitations. A call to a file positioning function, such as fseek(), will discard any character pushed back by ungetc(). Also, the C standard only guarantees that the pushing back of one character will succeed. ThereforeConsequently, subsequent calls to ungetc() must be separated by a call to a read function or a file-positioning function (which will discard any data pushed by ungetc()).
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