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In this non-compliant code example, more than one character is pushed back on the stream referenced by fptr fp.

FILE * fptrfp;
char *file_name;

/* initialize file_name */

fp = fopen(file_name, "rb");
if (fptrfp == NULL) {
  /* Handlehandle Error */
}

/* Readread data */

ungetc('\n', fptrfp);
ungetc('\r', fptrfp);

/* Continuecontinue on */

Compliant Solution

If more than one character needs to be pushed by ungetc(), then fgetpos() and fsetpos() should be used before and after reading the data instead of pushing it back with ungetc(). Note that this solution can only be used if the input is seekable.

FILE * fptrfp;
fpos_t pos;
char *file_name;

/* initialize file_name */

fp = fopen(file_name, "rb");
fpos_t pos;

if (fptrfp == NULL) {
  /* Handlehandle Error */
}

/* Readread data */

if (fgetpos(fptrfp, &pos)) {
  /* Handlehandle Error */
}

/* Readread the data that will be "pushed back" */

if (fsetpos(fptrfp, &pos)) {
  /* Handlehandle Error */
}

/* Continue on */

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