--- ./src/cpm.c~	1994-06-04 18:46:13.000000000 +0200
+++ ./src/cpm.c	2023-03-13 22:35:26.379615000 +0100
@@ -51,8 +51,9 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <signal.h>
+#include <stdlib.h>
+#include <unistd.h>
 #include "cpmio.h"
-#include "cpmfio.h"
 
 #define BIG	2147483647
 
@@ -75,12 +76,13 @@
 
 char *string;
 
+int
 main(argc, argv)
 	int	argc;
 	char	*argv[];
 {
 
-	char *cpmname, *unixname, *malloc();
+	char *cpmname, *unixname;
 	int xflag = 0, stat=0, Cflag = 0, Iflag = 0, Bflag = 0;
 
 	if (argc == 1)
@@ -314,13 +316,14 @@
 		exit(0);
 	}
 	if (tflag > 0) {
-		copy(cpmname, stdout, 0);
+		copy(cpmname, (char *)stdout, 0);
 		exit(0);
 	}
 }
 
-
+long
 number(big)
+	long big;
 {
 	register char *cs;
 	long n;
@@ -351,14 +354,15 @@
 
 	case '\0':
 		if (n >= big || n < 0) {
-			fprintf(stderr,"number: argument %D out of range\n", n);
+			fprintf(stderr,"number: argument %ld out of range\n", n);
 			exit(1);
 		}
 		return (n);
 	}
 }
 
-usage()
+void
+usage(void)
 {
 	printf("Usage: cpm [-i][-d][-p name][-c|C name1 name2] file-name\n");
 	printf("Disk geometry options:\n");
--- ./src/interact.c~	1994-05-01 23:08:18.000000000 +0200
+++ ./src/interact.c	2023-03-13 22:53:16.660087000 +0100
@@ -1,20 +1,24 @@
 /*	interact.c	1.8	83/07/27	*/
 #include <stdio.h>
+#include <string.h>
 #include "command.h"
 #include <setjmp.h>
 #include <signal.h>
+#include "cpmio.h"
 
 #define errinp { printf("??\n"); break; }
+#define index(s, c) strchr(s, c)
 
 jmp_buf	env;
 int	firsttime = 0;
 
-interact()
+int
+interact(void)
 
 {
 
-	int	i, intrpt();
-	char	cmd[80], *rest, *index();
+	int	i;
+	char	cmd[80], *rest;
 
 	for (;;) {
 		if (firsttime++ == 0) {
@@ -62,7 +66,7 @@
 			return(0);
 
 		case CMD_TYPE:
-			copy(rest, stdout, 0);
+			copy(rest, (char *)stdout, 0);
 			break;
 
 		case CMD_HELP:
@@ -90,7 +94,9 @@
  * just (long)jump back to command input mode
  */
 
-intrpt()
+void
+intrpt(signo)
+	int signo;
 {
 	firsttime = 0;
 	printf("\n");
--- ./src/gensktab.c~	2023-03-13 21:24:48.963957000 +0100
+++ ./src/gensktab.c	2023-03-13 22:28:27.370903000 +0100
@@ -1,8 +1,8 @@
 /*	gensktab.c	1.4	83/05/13	*/
 #include <stdio.h>
+#include <stdlib.h>
 #include "cpmio.h"
 
-extern int	skew;
 int	*skewtab;
 
 /*
@@ -12,11 +12,11 @@
  * accesses are attempted.
  */
 
-gen_sktab()
+void
+gen_sktab(void)
 {
 
 	int	*i, *j;
-	char	*malloc();
 
 	if (( skewtab = (int *) malloc(sectrk*4)) == NULL) {
 		fprintf(stderr, 
--- ./src/ffc.c~	1983-06-24 00:20:29.000000000 +0200
+++ ./src/ffc.c	2023-03-13 22:53:42.692364000 +0100
@@ -16,6 +16,7 @@
  * hs 10/29/82
  */
 
+int
 ffc(start, len, field)
 
 #ifndef VAX
--- ./src/cmdhdl.c~	1994-05-28 09:00:02.000000000 +0200
+++ ./src/cmdhdl.c	2023-03-13 21:59:35.088747000 +0100
@@ -2,6 +2,8 @@
 
 #include <ctype.h>
 #include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
 #include "cpmio.h"
 
 #ifndef HELPFILE
@@ -14,6 +16,7 @@
  * return the number of characters read.
  */
 
+int
 cmdinp(cmd)
 	char cmd[];
 {
@@ -58,6 +61,7 @@
 	"!! ",		2,	0,		/* 15 */
 	"" , 0 };
 
+int
 chkcmd(cmd)
 	char *cmd;
 
@@ -84,7 +88,8 @@
 		return (++index);
 }
 
-help()
+void
+help(void)
 {
 
 	FILE *fd, *fopen();
@@ -103,6 +108,7 @@
  * bad file name, otherwise 1.
  */
 
+int
 namesep(fname, name, ext)
 	char fname[], name[], ext[];
 {
@@ -125,7 +131,7 @@
 	} else {
 		if (fname[i] != ' ' && fname[i] != '\0') {
 			fprintf(stderr, "Illegal filename\n");
-			return (NULL);
+			return (0);
 		}
 	}
 #ifdef DEBUG
@@ -133,11 +139,12 @@
 #endif
 	if (!(isalnum(name[0]))) {
 		fprintf(stderr, "Illegal filename\n");
-		return(NULL);
+		return(0);
 	}
 	return(1);
 }
 
+void
 clean(str, len)
 char str[];
 int len;
--- ./src/extent.c~	1994-05-28 12:47:09.000000000 +0200
+++ ./src/extent.c	2023-03-13 22:45:10.645426000 +0100
@@ -1,8 +1,8 @@
 /*	extent.c	1.7	83/05/13	*/
 
 #include <stdio.h>
+#include <string.h>
 #include "cpmio.h"
-#include "cpmfio.h"
 
 /*
  * Allocate a new extent to the file pointed to by curext,
@@ -12,6 +12,7 @@
  * the index to the new extent.
  */
 
+int
 creext(curext)
 	int curext;
 {
@@ -44,6 +45,7 @@
  * return the new extent's index if found, otherwise NULL.
  */
 
+int
 getnext(cur)
 	C_FILE	*cur;
 {
@@ -67,5 +69,5 @@
 #endif
 			return (ind);
 		}
-	return (NULL);
+	return (0);
 }
--- ./src/cpmio.h~	1994-05-28 12:27:27.000000000 +0200
+++ ./src/cpmio.h	2023-03-13 22:50:35.766391000 +0100
@@ -34,3 +34,53 @@
 extern int	*bitmap, *skewtab;
 extern int 	bm_size;
 extern int	use16bitptrs;
+
+#include "cpmfio.h"
+
+int ffc(long, int, int);
+int alloc(void);
+void dbmap(char *);
+int blks_used(void);
+void build_bmap(void);
+int getblock(int, char[], int);
+int putblock(int, char[], int);
+int putpsect(int, int, char[]);
+int getpsect(int, int, char[]);
+int initcpm(char *);
+int c_close(C_FILE *);
+C_FILE *c_creat(char *, char *, int);
+void dispdir(void);
+void getdir(void);
+void savedir(void);
+int searchdir(char *, char *);
+int creext(int);
+int getnext(C_FILE *);
+int c_fillbuf(C_FILE *);
+int c_flush(C_FILE *);
+int c_flsbuf(int, C_FILE *);
+int c_write(C_FILE *, char *, int);
+int cmdinp(char[]);
+int chkcmd(char *);
+void help(void);
+int namesep(char[], char[], char[]);
+void clean(char[], int);
+C_FILE *c_open(char *, char *, int);
+void fnfound(char[], char[]);
+void copyc(char[], int);
+void copy(char[], char[], int);
+void copytext(C_FILE *, FILE *);
+void copybin(C_FILE *, FILE *);
+void usage(void);
+long number(long);
+void gen_sktab(void);
+int interact(void);
+void intrpt(int);
+void pip(char[], int);
+void pipc(char[], char[], int);
+void piptext(C_FILE *, FILE *);
+void pipbin(C_FILE *, FILE *);
+void delete(char *);
+void dump(char[]);
+void hexdump(C_FILE *);
+void printline(FILE *, int[], int);
+int Rename(char *);
--- ./src/copy.c~	1994-05-05 00:23:14.000000000 +0200
+++ ./src/copy.c	2023-03-13 22:06:10.049082000 +0100
@@ -1,8 +1,9 @@
 /*	copy.c	1.8	83/05/13	*/
 
 #include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
 #include "cpmio.h"
-#include "cpmfio.h"
 
 #define	CTRL_Z	0x1a		/* CP/M end-of-file */
 
@@ -10,6 +11,7 @@
  * copy cpmfile to unix file 
  */
 
+void
 copyc(cmdline, bin)
 	char cmdline[];
 {
@@ -24,10 +26,10 @@
 	copy(cmdline, i+1, bin);
 }
 
+void
 copy(cpmfile, unixfile, bin)
 	char cpmfile[], unixfile[];
 {
-	extern char *getenv();
 	FILE *ufid;
 	char name[9], ext[4];
 	char *pager = 0;
@@ -65,6 +67,7 @@
 		pclose(ufid);
 }
 
+void
 copytext(cid, ufid)
 	FILE *ufid;
 	C_FILE *cid;
@@ -81,6 +84,7 @@
 		fclose(ufid);
 }
 
+void
 copybin(cid, ufid)
 	FILE *ufid;
 	C_FILE *cid;
--- ./src/hexdmp.c~	1994-05-28 11:02:14.000000000 +0200
+++ ./src/hexdmp.c	2023-03-13 22:44:54.086889000 +0100
@@ -3,8 +3,8 @@
 #include <ctype.h>
 #include <stdio.h>
 #include "cpmio.h"
-#include "cpmfio.h"
 
+void
 dump(cmdline)
 	char cmdline[];
 {
@@ -23,6 +23,7 @@
 	c_close(cid);  
 }
 
+void
 hexdump(fp)
 	C_FILE *fp;
 {
@@ -56,9 +57,10 @@
 		pclose(piped);
 }
 
+void
 printline(piped, cbuf, nc)
 	FILE *piped;
-	int cbuf[];
+	int cbuf[], nc;
 {
 	int i1;
 
--- ./src/dirhdl.c~	1994-05-02 23:39:23.000000000 +0200
+++ ./src/dirhdl.c	2023-03-13 22:42:19.809668000 +0100
@@ -1,11 +1,14 @@
 /*	dirhdl.c	1.7	83/05/13	*/
 
 #include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
 #include "cpmio.h"
 
 /* Display cp/m directory on stdout */
 
-dispdir()
+void
+dispdir(void)
 {
 
 	int cnt, i;
@@ -39,7 +42,8 @@
 	return;
 }
 
-getdir()
+void
+getdir(void)
 
 {
 
@@ -50,7 +54,7 @@
 	if ((maxdir*32)%blksiz > 0) 
 		++blks;
 	for (bl = 0; blks > 0; bl++, blks--) {
-		if (getblock(bl,dirbuf+offset,-1) == EOF) {
+		if (getblock(bl,(char *)(dirbuf+offset),-1) == EOF) {
 			fprintf(stderr, "getdir: fatal error\n");
 			exit (0);
 		}
@@ -59,7 +63,8 @@
 }
 
 
-savedir()
+void
+savedir(void)
 
 {
 
@@ -70,7 +75,7 @@
 	if ((maxdir*32)%blksiz > 0) 
 		++blks;
 	for (bl = 0; blks > 0; bl++, blks--) {
-		if (putblock(bl,dirbuf+offset,-1) == EOF) {
+		if (putblock(bl,(char *)(dirbuf+offset),-1) == EOF) {
 			fprintf(stderr, "savedir: fatal error\n");
 			exit (0);
 		}
@@ -84,6 +89,7 @@
  * returned if found.
  */
 
+int
 searchdir(name,ext)
 char *name, *ext;
 
--- ./src/delete.c~	1983-06-24 00:19:48.000000000 +0200
+++ ./src/delete.c	2023-03-13 22:36:55.216932000 +0100
@@ -2,12 +2,12 @@
 
 #include <stdio.h>
 #include "cpmio.h"
-#include "cpmfio.h"
 
 /*
  * Delete cp/m file
  */
 
+void
 delete(cmdline)
 char *cmdline;
 
--- ./src/bitmap.c~	1994-05-28 08:52:55.000000000 +0200
+++ ./src/bitmap.c	2023-03-13 21:33:33.379559000 +0100
@@ -1,6 +1,7 @@
 /*	bitmap.c	1.9	83/05/13	*/
 
 #include <stdio.h>
+#include <stdlib.h>
 #include "cpmio.h"
 int	bm_size;
 
@@ -21,7 +22,7 @@
  * Allocate a new disk block, return NULL if disk full 
  */
 int
-alloc()
+alloc(void)
 
 {
 
@@ -47,6 +48,7 @@
  * Dump the bitmap in hex to stdout, used only for debugging 
  */
 
+void
 dbmap(str)
 	char *str;
 {
@@ -65,7 +67,8 @@
  * directory, including the directory blocks
  */
 
-blks_used()
+int
+blks_used(void)
 {
 
 	int j, i, temp;
@@ -89,10 +92,11 @@
 }
 
 
-build_bmap()
+void
+build_bmap(void)
 {
 
-	int	i, j, *malloc(), offset, block;
+	int	i, j, offset, block;
 
 	bm_size = 1 + ((seclth*sectrk*(tracks-restrk))/blksiz)/INTSIZE;
 
--- ./src/pip.c~	1983-06-24 00:20:48.000000000 +0200
+++ ./src/pip.c	2023-03-13 22:53:58.575346000 +0100
@@ -1,15 +1,17 @@
 /*	pip.c	1.5	83/05/13	*/
 
 #include <stdio.h>
+#include <unistd.h>
 #include "cpmio.h"
-#include "cpmfio.h"
 
 /*
  * Copy unix file to cpm
  */
 
+void
 pip(cmdline, bin)
 	char cmdline[];
+	int bin;
 {
 
 	char	*index(), *i;
@@ -22,8 +24,10 @@
 	pipc(cmdline,i+1, bin);
 }
 
+void
 pipc(unixfile, cpmfile, bin)
 	char cpmfile[], unixfile[];
+	int bin;
 {
 
 	FILE *ufid;
@@ -49,6 +53,7 @@
 	fclose(ufid);
 }
 
+void
 piptext(cid, ufid)
 	FILE *ufid;
 	C_FILE *cid;
@@ -65,6 +70,7 @@
 	}
 }
 
+void
 pipbin(cid, ufid)
 	FILE *ufid;
 	C_FILE *cid;
--- ./src/cclose.c~	1994-05-28 12:28:10.000000000 +0200
+++ ./src/cclose.c	2023-03-13 21:48:51.189287000 +0100
@@ -1,7 +1,7 @@
 /*	cclose.c	1.10	83/05/13	*/
 #include <stdio.h>
+#include <stdlib.h>
 #include "cpmio.h"
-#include "cpmfio.h"
 
 /*
  * Close cp/m file
@@ -9,6 +9,7 @@
  * buffer to disk and update directory 
  */
 
+int
 c_close(fptr)
 	register C_FILE *fptr;
 {
@@ -47,5 +48,5 @@
 	/* deallocate buffer memory and file descriptor */
 	fptr->c_flag = 0;
 	free(fptr->c_base);
-	return (NULL);
+	return (0);
 }
--- ./src/physio.c~	1994-05-04 00:47:23.000000000 +0200
+++ ./src/physio.c	2023-03-13 22:52:08.309089000 +0100
@@ -3,13 +3,16 @@
 #include <stdio.h>
 #include "cpmio.h"
 #include <fcntl.h>
+#include <unistd.h>
 
 /*
  * Write physical sector to floppy disk file
  */
 
+int
 putpsect(tr, sect, buf)
 	char buf[];
+	int tr, sect;
 {
 
 	long newpos;
@@ -35,8 +38,10 @@
  * Read physical sector from floppy disk file
  */
 
+int
 getpsect(tr, sect, buf)
 	char buf[];
+	int tr, sect;
 {
 
 	long newpos;
@@ -64,6 +69,7 @@
  * return its file pointer.
  */
 
+int
 initcpm(name)
 	char *name;
 {
--- ./src/blockio.c~	1994-05-02 23:24:00.000000000 +0200
+++ ./src/blockio.c	2023-03-13 21:39:57.913922000 +0100
@@ -9,8 +9,10 @@
  * if nsect is negative then always read a full block.
  */
 
+int
 getblock(blockno, buffer, nsect)
 	char buffer[];
+	int blockno, nsect;
 {
 
 	int sect, track, counter;
@@ -42,8 +44,10 @@
  * If nsects is negative, write a full block.
  */
 
+int
 putblock(blockno, buffer, nsect)
 	char buffer[];
+	int blockno, nsect;
 {
 
 	int sect, track, counter;
--- ./src/cfillbuf.c~	1994-05-04 00:45:39.000000000 +0200
+++ ./src/cfillbuf.c	2023-03-13 21:53:52.999972000 +0100
@@ -2,18 +2,18 @@
 
 #include <stdio.h>
 #include "cpmio.h"
-#include "cpmfio.h"
 
+int
 c_fillbuf(fptr)
 	register C_FILE *fptr;
 {
 
-	int	getnext(), nsect;
+	int	nsect;
 
 	if (++fptr->c_blk == (use16bitptrs? 8: 16))
 		if (fptr->c_dirp->blkcnt ==  (char) 0x80) {
 			/* find next extent (if it exists) */
-			if (getnext(fptr) == NULL)
+			if (getnext(fptr) == 0)
 				return (EOF);
 		}
 	else 
--- ./src/rename.c~	1994-05-01 23:08:50.000000000 +0200
+++ ./src/rename.c	2023-03-13 22:52:55.083376000 +0100
@@ -1,14 +1,15 @@
 /*	rename.c	1.8	83/05/13	*/
 
 #include <stdio.h>
+#include <string.h>
 #include "cpmio.h"
-#include "cpmfio.h"
 
 /*
  * Rename a cp/m file
  * returns: 1 = failure, 0 = success 
  */
 
+int
 Rename(cmdline)
 	char *cmdline;
 
@@ -34,7 +35,7 @@
 		do {
 			strncpy(cio->c_dirp->name, newname, 8);
 			strncpy(cio->c_dirp->ext, newext, 3);
-		} while (getnext(cio) != NULL);
+		} while (getnext(cio) != 0);
 	} else {
 		fnfound(oldname, oldext);
 		return (1);
--- ./src/copen.c~	1994-05-28 12:46:30.000000000 +0200
+++ ./src/copen.c	2023-03-13 22:00:48.175250000 +0100
@@ -1,8 +1,8 @@
 /*	copen.c	1.7	83/05/13	*/
 
 #include <stdio.h>
+#include <stdlib.h>
 #include "cpmio.h"
-#include "cpmfio.h"
 
 /*
  * Open cp/m file with the given file name and extension, return
@@ -18,7 +18,6 @@
 
 	int	i, index, scnt;
 	register C_FILE *fptr;
-	char *malloc();
 
 	if ((index = searchdir(name, ext)) == -1) {
 		fnfound(name, ext);
@@ -68,6 +67,7 @@
 	return (fptr);
 }
 
+void
 fnfound(name, ext)
 	char name[], ext[];
 {
--- ./src/ccreat.c~	1994-05-04 00:36:44.000000000 +0200
+++ ./src/ccreat.c	2023-03-13 21:52:02.090429000 +0100
@@ -1,7 +1,8 @@
 /*	ccreat.c	1.9	83/05/13	*/
 #include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
 #include "cpmio.h"
-#include "cpmfio.h"
 
 /*
  * Create cp/m file with the given file name and extension, return
@@ -16,14 +17,12 @@
 
 	int	i, index;
 	register C_FILE *fptr;
-	char *malloc();
-	int alloc();
 
 	if (searchdir(name, ext) != -1) {
 		fprintf(stderr, "file already exists: %s %s\n",name, ext);
 		return(NULL);
 	}
-	if ((index = creext(-1)) < NULL) {
+	if ((index = creext(-1)) < 0) {
 		fprintf(stderr, "c_creat: no directory space\n");
 		return (NULL);
 	}
--- ./src/cflsbuf.c~	1994-05-28 09:48:52.000000000 +0200
+++ ./src/cflsbuf.c	2023-03-13 21:56:11.480036000 +0100
@@ -2,7 +2,6 @@
 
 #include <stdio.h>
 #include "cpmio.h"
-#include "cpmfio.h"
 
 /*
  * Flush a full block to floppy disk file
@@ -11,12 +10,12 @@
  * Create a new extent if required
  */
 
+int
 c_flush(fptr)
 	register C_FILE *fptr;
 {
 
 	int	it; 
-	int	alloc();
 
 	if (!(fptr->c_flag & WRITE)) {
 		fprintf(stderr, "no write access");
@@ -31,7 +30,7 @@
 		fptr->c_dirp->blkcnt =  (char) 0x80;
 		savedir();
 		/* create new extent */
-		if ((it = creext(fptr->c_ext)) == NULL) {
+		if ((it = creext(fptr->c_ext)) == 0) {
 			fprintf(stderr,"can't create new extent, current: %d\n",
 				fptr->c_ext);
 			return (EOF);
@@ -57,6 +56,7 @@
 	return (0);
 }
 
+int
 c_flsbuf(c, fptr)
 	register C_FILE *fptr;
 {
@@ -72,6 +72,7 @@
  * flush the buffer if full (for binary file transfers)
  */
 
+int
 c_write(fptr, buf, cnt)
 	register C_FILE *fptr;
 	char *buf;
--- ./README~	1994-06-05 01:28:04.000000000 +0200
+++ ./README	2023-03-13 22:56:43.728910000 +0100
@@ -12,3 +12,13 @@
 
 Cpm lets UNIX users read and write standard cp/m 8" floppy disks and
 provides a cp/m like user interface for manipulating cp/m files.
+
+-----------
+
+Remark from 2023:
+
+This source code used to be compilable for about 40 years by now.
+Meanwhile, C compilers stopped to still tolerate "traditional" (=
+pre-C89) C source code, so a larger patch was needed to provide
+function prototypes for everything, and include the now standardized
+library header files.