Chapter Summary

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Writing to and reading from files is essential for most C programs. Most C implementations offer both low-level I/O services and standard high-level I/O services for these purposes. Because the ANSI C library includes the standard I/O services but not the low-level services, the standard package is more portable.

The standard I/O package automatically creates input and output buffers to speed up data transfer. The fopen() function opens a file for standard I/O and creates a data structure designed to hold information about the file and the buffer. The fopen() function returns a pointer to that data structure, and this pointer is used by other functions to identify the file to be processed . The feof() and ferror () functions report the reason an I/O operation failed.

ANSI C provides two file-opening modes: binary and text. When a file is opened in binary mode, it can be read byte-for-byte. When a file is opened in text mode, its contents may be mapped from the system representation of text to the C representation. For UNIX systems, the two modes are identical because the C model for text files is derived from the UNIX file model.

The input functions getc() , fgets() , fscanf() , and fread() normally read a file sequentially, starting at the beginning of the file. However, the fseek() and ftell () functions let a program move to an arbitrary position in a file, enabling random access. The fgetpos () and fsetpos () extend similar capabilities to larger files. Random access works better in the binary than in the text mode.

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