c/io/fopen

@1@ Opens a file indicated by and returns a pointer to the file stream associated with that file. is used to determine the file access mode. @2@ Same as, except that the pointer to the file stream is written to and the following errors are detected at runtime and call the currently installed constraint handler function:
 * is a null pointer
 * is a null pointer
 * is a null pointer

Return value
@1@ If successful, returns a pointer to the new file stream. The stream is fully buffered unless refers to an interactive device. On error, returns a null pointer. POSIX requires that errno be set in this case.

@2@ If successful, returns zero and a pointer to the new file stream is written to. On error, returns a non-zero error code and writes the null pointer to (unless  is a null pointer itself).