github.com/afumu/libc@v0.0.6/musl/src/stdio/setvbuf.c (about)

     1  #include "stdio_impl.h"
     2  
     3  /* The behavior of this function is undefined except when it is the first
     4   * operation on the stream, so the presence or absence of locking is not
     5   * observable in a program whose behavior is defined. Thus no locking is
     6   * performed here. No allocation of buffers is performed, but a buffer
     7   * provided by the caller is used as long as it is suitably sized. */
     8  
     9  int setvbuf(FILE *restrict f, char *restrict buf, int type, size_t size)
    10  {
    11  	f->lbf = EOF;
    12  
    13  	if (type == _IONBF) {
    14  		f->buf_size = 0;
    15  	} else if (type == _IOLBF || type == _IOFBF) {
    16  		if (buf && size >= UNGET) {
    17  			f->buf = (void *)(buf + UNGET);
    18  			f->buf_size = size - UNGET;
    19  		}
    20  		if (type == _IOLBF && f->buf_size)
    21  			f->lbf = '\n';
    22  	} else {
    23  		return -1;
    24  	}
    25  
    26  	f->flags |= F_SVB;
    27  
    28  	return 0;
    29  }