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Write into a file without changing the file pointer
#include <unistd.h> ssize_t pwrite( int filedes, const void* buff, size_t nbytes, off_t offset ); ssize_t pwrite64( int filedes, const void* buff, size_t nbytes, off64_t offset );
- The file descriptor for the file you want to write in.
- A pointer to a buffer that contains the data you want to write.
- The number of bytes to write.
- The desired position inside the file.
Use the -l c option to qcc to link against this library. This library is usually included automatically.
The pwrite() function performs the same action as write(), except that it writes into a given position without changing the file pointer.
The pwrite64() function is a 64-bit version of pwrite().
The number of bytes actually written, or -1 if an error occurred (errno is set).
- The O_NONBLOCK flag is set for the file descriptor, and the process would be delayed in the write operation.
- The file descriptor, fildes, isn't a valid file descriptor open for writing.
- File is too big.
- The write operation was interrupted by a signal, and either no data was transferred, or the resource manager responsible for that file doesn't report partial transfers.
- A physical I/O error occurred (for example, a bad block on a disk). The precise meaning is device-dependent.
- There's no free space remaining on the device containing the file.
- The pwrite() function isn't implemented for the filesystem specified by filedes.
- An attempt was made to write to a pipe (or FIFO) that isn't open for reading by any process. A SIGPIPE signal is also sent to the process.