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getcwd, getwd, get_current_dir_name - get current working directory
#include <unistd.h> char *getcwd(char *buf, size_t size); char *getwd(char *buf); char *get_current_dir_name(void); Feature Test Macro Requirements for glibc (see feature_test_macros(7)): get_current_dir_name(): _GNU_SOURCE getwd(): Since glibc 2.12: _BSD_SOURCE || (_XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED) && !(_POSIX_C_SOURCE >= 200809L || _XOPEN_SOURCE >= 700) Before glibc 2.12: _BSD_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
These functions return a null-terminated string containing an absolute pathname that is the current working directory of the calling process. The pathname is returned as the function result and via the argument buf, if present. If the current directory is not below the root directory of the current process (e.g., because the process set a new filesystem root using chroot(2) without changing its current directory into the new root), then, since Linux 2.6.36, the returned path will be prefixed with the string "(unreachable)". Such behavior can also be caused by an unprivileged user by changing the current directory into another mount namespace. When dealing with paths from untrusted sources, callers of these functions should consider checking whether the returned path starts with '/' or '(' to avoid misinterpreting an unreachable path as a relative path. The getcwd() function copies an absolute pathname of the current working directory to the array pointed to by buf, which is of length size. If the length of the absolute pathname of the current working directory, including the terminating null byte, exceeds size bytes, NULL is returned, and errno is set to ERANGE; an application should check for this error, and allocate a larger buffer if necessary. As an extension to the POSIX.1-2001 standard, glibc's getcwd() allocates the buffer dynamically using malloc(3) if buf is NULL. In this case, the allocated buffer has the length size unless size is zero, when buf is allocated as big as necessary. The caller should free(3) the returned buffer. get_current_dir_name() will malloc(3) an array big enough to hold the absolute pathname of the current working directory. If the environment variable PWD is set, and its value is correct, then that value will be returned. The caller should free(3) the returned buffer. getwd() does not malloc(3) any memory. The buf argument should be a pointer to an array at least PATH_MAX bytes long. If the length of the absolute pathname of the current working directory, including the terminating null byte, exceeds PATH_MAX bytes, NULL is returned, and errno is set to ENAMETOOLONG. (Note that on some systems, PATH_MAX may not be a compile-time constant; furthermore, its value may depend on the filesystem, see pathconf(3).) For portability and security reasons, use of getwd() is deprecated.
On success, these functions return a pointer to a string containing the pathname of the current working directory. In the case getcwd() and getwd() this is the same value as buf. On failure, these functions return NULL, and errno is set to indicate the error. The contents of the array pointed to by buf are undefined on error.
EACCES Permission to read or search a component of the filename was denied. EFAULT buf points to a bad address. EINVAL The size argument is zero and buf is not a null pointer. EINVAL getwd(): buf is NULL. ENAMETOOLONG getwd(): The size of the null-terminated absolute pathname string exceeds PATH_MAX bytes. ENOMEM Out of memory. ENOENT The current working directory has been unlinked. ERANGE The size argument is less than the length of the absolute pathname of the working directory, including the terminating null byte. You need to allocate a bigger array and try again.
For an explanation of the terms used in this section, see attributes(7). ┌───────────────────────┬───────────────┬─────────────┐ │Interface │ Attribute │ Value │ ├───────────────────────┼───────────────┼─────────────┤ │getcwd(), getwd() │ Thread safety │ MT-Safe │ ├───────────────────────┼───────────────┼─────────────┤ │get_current_dir_name() │ Thread safety │ MT-Safe env │ └───────────────────────┴───────────────┴─────────────┘
getcwd() conforms to POSIX.1-2001. Note however that POSIX.1-2001 leaves the behavior of getcwd() unspecified if buf is NULL. getwd() is present in POSIX.1-2001, but marked LEGACY. POSIX.1-2008 removes the specification of getwd(). Use getcwd() instead. POSIX.1-2001 does not define any errors for getwd(). get_current_dir_name() is a GNU extension.
Under Linux, the function getcwd() is a system call (since 2.1.92). On older systems it would query /proc/self/cwd. If both system call and proc filesystem are missing, a generic implementation is called. Only in that case can these calls fail under Linux with EACCES. These functions are often used to save the location of the current working directory for the purpose of returning to it later. Opening the current directory (".") and calling fchdir(2) to return is usually a faster and more reliable alternative when sufficiently many file descriptors are available, especially on platforms other than Linux.
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