PHP4 User manual: Function-fwrite

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(PHP 3, PHP 4 >= 4.0.0)
Fwrite--Binary file write
Describe

int fwrite (int fp, string string [, int length])

Fwrite () writes the contents of string strings to the file stream specified by the FP. If length is given, the byte specified by length is written and ends after.
Note that if the length parameter is given, the magic_quotes_runtime configuration option will be ignored and the "" in the string will not be deleted.
Note: On some systems, the binary and text files (i.e. Windows) will be distinguished, and this file must be opened using the fopen () of the pattern with the ' B ' parameter.
See Fread (), fopen (), Fsockopen (), Popen (), and fputs ().