GNU/Linux man pages
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GNU/Linux |
CentOS 4.8 |
i386 |
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getwd(3) |
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getcwd, get_current_dir_name, getwd − Get current working directory
#include <unistd.h>
char
*getcwd(char *buf, size_t size);
char *get_current_dir_name(void);
char *getwd(char *buf);
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 current absolute path name would require a buffer longer than size elements, NULL is returned, and errno is set to ERANGE; an application should check for this error, and allocate a larger buffer if necessary.
If buf is NULL, the behaviour of getcwd() is undefined.
As an extension to the POSIX.1 standard, Linux (libc4, libc5, glibc) getcwd() allocates the buffer dynamically using malloc() if buf is NULL on call. In this case, the allocated buffer has the length size unless size is zero, when buf is allocated as big as necessary. It is possible (and, indeed, advisable) to free() the buffers if they have been obtained this way.
get_current_dir_name, which is only prototyped if _GNU_SOURCE is defined, will malloc(3) an array big enough to hold the current directory name. If the environment variable PWD is set, and its value is correct, then that value will be returned.
getwd, which is only prototyped if _BSD_SOURCE or _XOPEN_SOURCE_EXTENDED is defined, will not malloc(3) any memory. The buf argument should be a pointer to an array at least PATH_MAX bytes long. getwd does only return the first PATH_MAX bytes of the actual pathname. Note that PATH_MAX need not be a compile-time constant; it may depend on the filesystem and may even be unlimited. For portability and security reasons, use of getwd is deprecated.
NULL on failure with errno set accordingly, and buf on success. The contents of the array pointed to by buf is undefined on error.
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EACCES |
Permission to read or search a component of the file name was denied. | ||
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EFAULT |
buf points to a bad address. | ||
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EINVAL |
The size argument is zero and buf is not a null pointer. | ||
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ENOENT |
The current working directory has been unlinked. | ||
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ERANGE |
The size argument is less than the length of the working directory name. You need to allocate a bigger array and try again. |
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 file system 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.
POSIX.1
chdir(2), fchdir(2), open(2), unlink(2), free(3), malloc(3)
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getwd(3) | |