Boost filesystem check file exists

Source code for each of the tutorial programs is available, and you are encouraged to compile, test, and experiment with it. To conserve space, we won't always show boilerplate code here, but the provided source is complete and ready to build.

Install the Boost distribution if you haven't already done so. See the Boost Getting Started docs. This tutorial assumes you are going to compile and test the examples using the provided scripts. That's highly recommended.

If you are planning to compile and test the examples but not use the scripts, make sure your build setup knows where to locate or build the Boost library binaries. If the tut1 command outputs " Usage: tut1 path ", all is well. You are encouraged to modify and experiment with them as the tutorial progresses. Just invoke the build script again to rebuild, or invoke b2 directly. Let's get started. Our first example program, tut1.

The Boost. The declaration looks like this:. If you can't wait to find out more, skip ahead to the class path section of the tutorial. Please take a minute to try out tut1 on your system, using a file that is known to exist, such as tut1. Here is what the results look like on two different operating systems:. So far, so good. The sizes reported may differ from the above if changes have been made to tut1. An exception is thrown; the exact form of the response depends on Windows system options.

What happens? There's no file named foo in the current directory, so by default an exception is thrown. See Error reporting to learn about error reporting via error codes rather than exceptions. These return bool 's, and will return true if the condition described by their name is met.

Otherwise they return false , including when any element of the path argument can't be found. Although tut2 works OK in these tests, the output is less than satisfactory for a directory. We'd typically like to see a list of the directory's contents. In tut3. End users shouldn't have to interpret cryptic exceptions reports, so as we move on to tut3.

Constructed from a path, it iterates over the contents of the directory. See Getting Started. These source files implement the library for POSIX or Windows compatible operating systems; no implementation is supplied for other operating systems.

Note that many operating systems not normally thought of as POSIX systems, such as mainframe legacy operating systems or embedded operating systems, support POSIX compatible file systems which will work with the Filesystem Library. See the Separate Compilation page for a description of the techniques used. The library's implementation code automatically detects the current platform, and compiles the POSIX or Windows implementation code accordingly.

With the exception of the Cygwin environment, there is usually no reason to define these macros, as the software development kits supplied with most compilers only support a single platform. The Cygwin package of tools supports traditional Windows usage, but also provides an emulation layer and other tools which can be used to make Windows act as Linux and thus POSIX , and provide the Linux look-and-feel.

GCC is usually the compiler of choice in this environment, as it can be installed via the Cygwin install process. Filesystem's object-library. The Filesystem Library was designed and implemented by Beman Dawes. Thomas Witt was a particular help in later stages of initial development. Peter Dimov and Rob Stewart made many useful suggestions and comments over a long period of time. Howard Hinnant helped with internationalization issues. Key design requirements and design realities were developed during extensive discussions on the Boost mailing list, followed by comments on the initial implementation.

Numerous helpful comments were then received during the Formal Review. So many people have contributed comments and bug reports that it isn't any longer possible to acknowledge them individually. That said, Peter Dimov and Rob Stewart need to be specially thanked for their many constructive criticisms and suggestions. Terence Wilson and Chris Frey contributed timing programs which helped illuminate performance issues. Use, modification, and distribution are subject to the Boost Software License, Version 1.

See www. Introduction Using the library Two-minute tutorial Cautions Example programs Implementation Macros Deprecated names and features Using only narrow character paths Building the object-library Notes for Cygwin users Acknowledgements Change history. Defined if Windows is detected by Boost.

System's automatic configuration code, otherwise not defined. Defined if Windows is not detected by Boost. Thus equivalent "foo", "bar" will be true when both paths resolve to the same file. Programmers wishing to determine if two paths are "the same" must decide if "the same" means "the same representation" or "resolve to the same actual file", and choose the appropriate function accordingly.

The inserter and extractor delimit the string with double-quotes " to ensure that paths with embedded spaces will round trip correctly. Returns: Reference to copy of p1 stored by the constructor, or, if none, an empty path. Returns: Reference to copy of p2 stored by the constructor, or, if none, an empty path. The exact format is unspecified. Implementations are encouraged but not required to include path1. This enum specifies bitmask constants uses to identify file permissions.

There is much variation in how operating systems treat symlinks. Windows: All permissions except write are currently ignored. There is only a single write permission; setting write permission for owner, group, or others sets write permission for all, and removing write permission for owner, group, or others removes write permission for all.

Meaningless on Windows as permissions never resolves symlinks. Get over it. Caching such status information can result is significant time savings. Cached and non-cached results may differ in the presence of file system races.

Actual cold-boot timing of iteration over a directory with 15, entries was six seconds for non-cached status queries versus one second for cached status queries. Windows XP, 3. Similar speedups are expected on Linux and BSD-derived systems that provide status as a by-product of directory iteration.

If the end of the directory elements is reached, the iterator becomes equal to the end iterator value. Directory iteration shall not yield directory entries for the current dot and parent dot dot directories.

It could be a symbolic link to a non-existent file. Programs recursively walking directory trees for purposes of removing and renaming entries may wish to avoid following symbolic links. Effects: Constructs a iterator representing the first entry in the directory p resolves to, if any; otherwise, the end iterator. Operational functions access a file by resolving an object of class path to a particular file in a file hierarchy.

See Error reporting. Returns: A absolute path composed according to the following table. Throws: If base. Overview: Converts p , which must exist, to an absolute path that has no symbolic link, dot , or dot-dot elements. Returns: A canonical path that refers to the same file system object as absolute p,base. Effects: Creates directory to , with attributes copied from directory from. The set of attributes copied is operating system dependent. Otherwise, the contents and attributes of the file from resolves to are copied to the file to resolves to.

Returns: true if a new directory was created, otherwise false. Creation failure because p resolves to an existing directory shall not be treated as an error. Some file systems do not support symbolic links regardless of the operating system - the FAT file system used on memory cards and flash drives, for example. Some file systems do not support hard links regardless of the operating system - the FAT file system used on memory cards and flash drives, for example.

Some file systems limit the number of links per file. Some file systems do not support symbolic links regardless of the operating system - the FAT system used on memory cards and flash drives, for example. The current path as returned by many operating systems is a dangerous global variable. It may be changed unexpectedly by a third-party or system library functions, or by another thread. Returns: exists status p or exists status p, ec , respectively. If ec! Two paths are considered to resolve to the same file system entity if two candidate entities reside on the same device at the same location.

Throws: For the first call, as specified in Error reporting. Subsequent calls throw nothing. Effects: Sets ec as if by status p, ec. To distinguish between cases, call the status function directly. The effective permission bits are determined as specified by the following table. Returns: If p resolves to a symbolic link, a path object containing the contents of that symbolic link. Otherwise an empty path object. Throws: As specified in Error reporting. Returns: false if p did not exist in the first place, otherwise true.

A symbolic link is itself renamed, rather than the file it resolves to being renamed. Any members for which the value cannot be determined shall be set to These distinctions are important to some use cases. Remarks: If a symbolic link is encountered during pathname resolution, pathname resolution continues using the contents of the symbolic link.

Effects: Composes an absolute path from p , using the same rules used by the operating system to resolve a path passed as the filename argument to standard library open functions. Postcondition: For the returned path, rp, rp. Otherwise it acts like complete p, kinky , where kinky is the current directory for the p. This will be the current directory of that drive the last time it was set, and thus may be residue left over from a prior program run by the command processor! Although these semantics are often useful, they are also very error-prone.

See complete note for usage suggestions. Returns: A directory path suitable for temporary files under the conventions of the operating system. The specifics of how this path is determined are implementation defined. An error shall be reported if! The name is based on a model that uses the percent sign character to specify replacement by a random hexadecimal digit.