Партнёры:
Хостинг:
getcwd - get the pathname of the current working directory
#include <unistd.h>
char *getcwd(char *buf, size_t size);
The getcwd() function shall place an absolute pathname of the current working directory in the array pointed to by buf, and return buf. The pathname copied to the array shall contain no components that are symbolic links. The size argument is the size in bytes of the character array pointed to by the buf argument. If buf is a null pointer, the behavior of getcwd() is unspecified.
Upon successful completion, getcwd() shall return the buf argument. Otherwise, getcwd() shall return a null pointer and set errno to indicate the error. The contents of the array pointed to by buf are then undefined.
The getcwd() function shall fail if:
The getcwd() function may fail if:
The following sections are informative.
The following example returns a pointer to an array that holds the absolute pathname of the current working directory. The pointer is returned in the ptr variable, which points to the buf array where the pathname is stored.
#include <stdlib.h>
#include <unistd.h>
...
long size;
char *buf;
char *ptr;
size = pathconf(".", _PC_PATH_MAX);
if ((buf = (char *)malloc((size_t)size)) != NULL)
ptr = getcwd(buf, (size_t)size);
...
Since the maximum pathname length is arbitrary unless {PATH_MAX} is defined, an application generally cannot supply a buf with size {{PATH_MAX}+1}.
Having getcwd() take no arguments and instead use the malloc() function to produce space for the returned argument was considered. The advantage is that getcwd() knows how big the working directory pathname is and can allocate an appropriate amount of space. But the programmer would have to use the free() function to free the resulting object, or each use of getcwd() would further reduce the available memory. Also, malloc() and free() are used nowhere else in this volume of IEEE Std 1003.1-2001. Finally, getcwd() is taken from the SVID where it has the two arguments used in this volume of IEEE Std 1003.1-2001.
The older function getwd() was rejected for use in this context because it had only a buffer argument and no size argument, and thus had no way to prevent overwriting the buffer, except to depend on the programmer to provide a large enough buffer.
On some implementations, if buf is a null pointer, getcwd() may obtain size bytes of memory using malloc(). In this case, the pointer returned by getcwd() may be used as the argument in a subsequent call to free(). Invoking getcwd() with buf as a null pointer is not recommended in conforming applications.
If a program is operating in a directory where some (grand)parent directory does not permit reading, getcwd() may fail, as in most implementations it must read the directory to determine the name of the file. This can occur if search, but not read, permission is granted in an intermediate directory, or if the program is placed in that directory by some more privileged process (for example, login). Including the [EACCES] error condition makes the reporting of the error consistent and warns the application writer that getcwd() can fail for reasons beyond the control of the application writer or user. Some implementations can avoid this occurrence (for example, by implementing getcwd() using pwd, where pwd is a set-user-root process), thus the error was made optional. Since this volume of IEEE Std 1003.1-2001 permits the addition of other errors, this would be a common addition and yet one that applications could not be expected to deal with without this addition.
malloc() , the Base Definitions volume of IEEE Std 1003.1-2001, <unistd.h>
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