Output isĪlways appended to the end of the file. The file is created if it does not exist. The stream is positioned atĪ+ Open for reading and appending (writing at end of file). The stream isĪ Open for appending (writing at end of file). The file is created if itĭoes not exist, otherwise it is truncated. The stream is positioned at the beginning of the W Truncate file to zero length or create text file for The argument mode points to a string beginning with one of theįollowing sequences (possibly followed by additional characters, Pointed to by pathname and associates a stream with it. The fopen() function opens the file whose name is the string SYNOPSIS top #include FILE *fopen(const char *restrict pathname, const char *restrict mode ) FILE *fdopen(int fd, const char * mode ) FILE *freopen(const char *restrict pathname, const char *restrict mode, FILE *restrict stream ) įeature Test Macro Requirements for glibc (see Linux), this is not an issue, because on those platforms, there is no difference between text mode and binary mode.Fopen(3) Library Functions Manual fopen(3) NAME topįopen, fdopen, freopen - stream open functions Therefore, the results you get will not be consistent. However, on Microsoft Windows, the characters \r\n (carriage return followed by line feed) will be translated to \n for text streams (but not for binary streams), so that the file size you get will count \r\n as two bytes, although you are only reading a single character ( \n) in text mode. That being said, on most common platforms, the posted code will work, if we assume that the data type long is large enough to represent the size of the file. The posted code is also not guaranteed to work on binary streams, because according to §7.21.9.2 ♣ of the ISO C11 standard, binary streams are not required to meaningfully support SEEK_END. There is no such guarantee for text streams. Only for binary streams is this value guaranteed to be the number of characters from the beginning of the file. The posted code is not guaranteed to work on text streams, because according to §7.21.9.4 ♢ of the ISO C11 standard, the value of the file position indicator returned by ftell contains unspecified information. In contrast to what other answers have suggested, the following code is not guaranteed to work: fseek( fp, 0, SEEK_END ) Įven if we assume that the data type long is large enough to represent the file size (which is questionable on some platforms, most notably Microsoft Windows), the posted code has the following problems:
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