upstream/mercurial-mirror Files · contrib/chg/util.h

posix: always seek to EOF when opening a file in append mode...

posix: always seek to EOF when opening a file in append mode Python 3 already does this, so skip it there. Consider the program: #include <stdio.h> int main() { FILE *f = fopen("narf", "w"); fprintf(f, "narf\n"); fclose(f); f = fopen("narf", "a"); printf("%ld\n", ftell(f)); fprintf(f, "troz\n"); printf("%ld\n", ftell(f)); return 0; } on macOS, FreeBSD, and Linux with glibc, this program prints 5 10 but on musl libc (Alpine Linux and probably others) this prints 0 10 By my reading of https://pubs.opengroup.org/onlinepubs/009695399/functions/fopen.html this is technically correct, specifically: > Opening a file with append mode (a as the first character in the > mode argument) shall cause all subsequent writes to the file to be > forced to the then current end-of-file, regardless of intervening > calls to fseek(). in other words, the file position doesn't really matter in append-mode files, and we can't depend on it being at all meaningful unless we perform a seek() before tell() after open(..., 'a'). Experimentally after a .write() we can do a .tell() and it'll always be reasonable, but I'm unclear from reading the specification if that's a smart thing to rely on. This matches what we do on Windows and what Python 3 does for free, so let's just be consistent. Thanks to Yuya for the idea.

Augie Fackler - - Load All Authors

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                r42778:97ada9b8

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        Yuya Nishihara
    
chg: import frontend sources...

              r28060
            
      /*

       * Utility functions

       *

       * Copyright (c) 2011 Yuya Nishihara <yuya@tcha.org>

       *

       * This software may be used and distributed according to the terms of the

       * GNU General Public License version 2 or any later version.

       */

      #ifndef UTIL_H_

      #define UTIL_H_

      #ifdef __GNUC__

      #define PRINTF_FORMAT_ __attribute__((format(printf, 1, 2)))

        Yuya Nishihara
    
chg: silence warning of unused parameter 'sig'

              r29440
            
      #define UNUSED_ __attribute__((unused))

        Jun Wu
    
chg: define PRINTF_FORMAT_ for non gnu C compiler...

              r28604
            
      #else

      #define PRINTF_FORMAT_

        Yuya Nishihara
    
chg: silence warning of unused parameter 'sig'

              r29440
            
      #define UNUSED_

        Yuya Nishihara
    
chg: import frontend sources...

              r28060
            
      #endif

      void abortmsg(const char *fmt, ...) PRINTF_FORMAT_;

        Jun Wu
    
chg: add util function abortmsgerrno to print error with errno...

              r28788
            
      void abortmsgerrno(const char *fmt, ...) PRINTF_FORMAT_;

        Yuya Nishihara
    
chg: import frontend sources...

              r28060
            
        Jun Wu
    
chg: use color in debug/error messages conditionally...

              r28787
            
      void enablecolor(void);

        Yuya Nishihara
    
chg: import frontend sources...

              r28060
            
      void enabledebugmsg(void);

      void debugmsg(const char *fmt, ...) PRINTF_FORMAT_;

        Jun Wu
    
chg: add fchdirx as a utility function...

              r28854
            
      void fchdirx(int dirfd);

        Jun Wu
    
chg: extract the logic of setting FD_CLOEXEC to a utility function...

              r28855
            
      void fsetcloexec(int fd);

        Jun Wu
    
chg: add utility functions mallocx, reallocx...

              r28165
            
      void *mallocx(size_t size);

      void *reallocx(void *ptr, size_t size);

        Yuya Nishihara
    
chg: import frontend sources...

              r28060
            
      int runshellcmd(const char *cmd, const char *envp[], const char *cwd);

        Augie Fackler
    
chg: enable clang-format on all .c and .h files...

              r35977
            
      #endif /* UTIL_H_ */

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Yuya Nishihara chg: import frontend sources...	r28060	/*
		* Utility functions
		*
		* Copyright (c) 2011 Yuya Nishihara <yuya@tcha.org>
		*
		* This software may be used and distributed according to the terms of the
		* GNU General Public License version 2 or any later version.
		*/

		#ifndef UTIL_H_
		#define UTIL_H_

		#ifdef __GNUC__
		#define PRINTF_FORMAT_ __attribute__((format(printf, 1, 2)))
Yuya Nishihara chg: silence warning of unused parameter 'sig'	r29440	#define UNUSED_ __attribute__((unused))
Jun Wu chg: define PRINTF_FORMAT_ for non gnu C compiler...	r28604	#else
		#define PRINTF_FORMAT_
Yuya Nishihara chg: silence warning of unused parameter 'sig'	r29440	#define UNUSED_
Yuya Nishihara chg: import frontend sources...	r28060	#endif

		void abortmsg(const char *fmt, ...) PRINTF_FORMAT_;
Jun Wu chg: add util function abortmsgerrno to print error with errno...	r28788	void abortmsgerrno(const char *fmt, ...) PRINTF_FORMAT_;
Yuya Nishihara chg: import frontend sources...	r28060
Jun Wu chg: use color in debug/error messages conditionally...	r28787	void enablecolor(void);
Yuya Nishihara chg: import frontend sources...	r28060	void enabledebugmsg(void);
		void debugmsg(const char *fmt, ...) PRINTF_FORMAT_;

Jun Wu chg: add fchdirx as a utility function...	r28854	void fchdirx(int dirfd);
Jun Wu chg: extract the logic of setting FD_CLOEXEC to a utility function...	r28855	void fsetcloexec(int fd);
Jun Wu chg: add utility functions mallocx, reallocx...	r28165	void *mallocx(size_t size);
		void reallocx(void ptr, size_t size);

Yuya Nishihara chg: import frontend sources...	r28060	int runshellcmd(const char cmd, const char envp[], const char *cwd);

Augie Fackler chg: enable clang-format on all .c and .h files...	r35977	#endif /* UTIL_H_ */