ferror
From cppreference.com
                    
                                        
                    
                    
                                                            
                    |   Defined in header  <stdio.h>
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|   int ferror( FILE *stream );  | 
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Checks the given stream for errors.
Parameters
| stream | - | the file stream to check | 
Return value
Nonzero value if the file stream has errors occurred, 0 otherwise
Example
Run this code
#include <stdio.h> #include <stdlib.h> #include <locale.h> #include <wchar.h> int main(void) { char* fname = tmpnam(NULL); FILE* f = fopen(fname, "wb"); fputs("\xff\xff\n", f); // not a valid UTF-8 character sequence fclose(f); setlocale(LC_ALL, "en_US.utf8"); f = fopen(fname, "rb"); wint_t ch; while ((ch=fgetwc(f)) != WEOF) // attempt to read as UTF-8 fails printf("%#x ", ch); if (feof(f)) puts("EOF indicator set"); if (ferror(f)) puts("Error indicator set"); }
Output:
Error indicator set