strerror() manipulation returns the value of errnum, generating a string describing the error that usually displaying that errno value in function calls.

   char * strerror ( int errnum );

   #include <iostream.h>
   #include <cstdio.h>
   #include <cstring.h>
   #include <errno.h>
   int main ()
     {
        FILE * str;
        str = fopen ("abdcf.bin","r+");
        if (str == NULL)
           printf ("ERROR opening file:: %s\n",strerror(errno));
        return 0;
     }

    ERROR opening file:: No such file or directory

In the above example, this manipulation function is used to display the error description and errno during function calls, when an unexisting file is opened using fopen().