Question

我目前正在编写一个C程序，用于读取和写入大小超过2 GiB的文件。在linux上 feature_test_macros （7）指定：

   _LARGEFILE64_SOURCE
          Expose definitions for the alternative API specified by the LFS (Large File Summit) as a  "tran‐
          sitional  extension"  to  the  Single  UNIX  Specification.  (See ⟨http://opengroup.org/platform
          /lfs.html⟩) The alternative API consists of a set of new objects  (i.e.,  functions  and  types)
          whose names are suffixed with "64" (e.g., off64_t versus off_t, lseek64() versus lseek(), etc.).
          New programs should not employ this interface; instead _FILE_OFFSET_BITS=64 should be employed.

   _FILE_OFFSET_BITS
          Defining this macro with the value 64 automatically converts references to 32-bit functions  and
          data  types related to file I/O and file system operations into references to their 64-bit coun‐
          terparts.  This is useful for performing I/O on large files (> 2 Gigabytes) on  32-bit  systems.
          (Defining  this macro permits correctly written programs to use large files with only a recompi‐
          lation being required.)  64-bit systems naturally permit file sizes greater  than  2  Gigabytes,
          and on those systems this macro has no effect.

这是否可以保证便携？

Solaris在 lfcompile （5）中建议：

 Applications can be compiled in the large  file  compilation
 environment by using the following methods:

     o    Use the getconf(1) utility with one or more of  the
          arguments listed in the table below. This method is
          recommended for portable applications.

          ____________________________________________________________
         |     argument     |                 purpose                |
         |__________________|________________________________________|
         | LFS_CFLAGS       |  obtain compilation flags necessary  to|
         |                  |  enable   the  large  file  compilation|
         |                  |  environment                           |
         | LFS_LDFLAGS      |  obtain link editor options            |
         | LFS_LIBS         |  obtain link library names             |
         | LFS_LINTFLAGS    |  obtain lint options                   |
         |__________________|________________________________________|

     o    Set the compile-time flag _FILE_OFFSET_BITS  to  64
          before including any headers. Applications may com-
          bine objects produced in the large file compilation
          environment  with  objects  produced in the transi-
          tional compilation environment, but must be careful
          with  respect  to  interoperability  between  those
          objects. Applications  should  not  declare  global
          variables of types whose sizes change between  com-
          pilation environments.

这可移植吗？在我的linux机器上，将这些键传递给 getconf 将不会输出任何内容。（这意味着密钥存在）。

有没有便携式方法？

Answer 1

使用confstr interface或相应的getconf program并尝试各种_CS_POSIX_V7_ILP32_OFFBIG_CFLAGS等选项，直到找到有效的选项。这将为您提供适当环境所需的CFLAGS，LDFLAGS和LIBS。

如何打开大文件支持？

1 个答案: