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Contents
Character Input Functions
The fgetc function
#include <stdio.h>
int fgetc(FILE *stream);
The fgetc function obtains the next character (if present) as an unsigned char converted to an int, from the input stream pointed to by stream, and advances the associated file position indicator for the stream (if defined).
The fgetc function returns the next character from the input stream pointed to by stream. If the stream is at end-of-file, the end-of-file indicator for the stream is set and fgetc returns EOF (EOF is a negative value defined in <stdio.h>, usually (-1)). If a read error occurs, the error indicator for the stream is set and fgetc returns EOF.
#include <stdio.h>
char *fgets(char *s, int n, FILE *stream);
The fgets function reads at most one less than the number of characters specified by n from the stream pointed to by stream into the array pointed to by s. No additional characters are read after a new-line character (which is retained) or after end-of-file. A null character is written immediately after the last character read into the array.
The fgets function returns s if successful. If end-of-file is encountered and no characters have been read into the array, the contents of the array remain unchanged and a null pointer is returned. If a read error occurs during the operation, the array contents are indeterminate and a null pointed is returned.
Warning: Different operating systems may use different character sequences to represent the end-of-line sequence. For example, some filesystems use the terminator \r\n in text files; fgets may read those lines, removing the \n but keeping the \r as the last character of s. This expurious character should be removed in the string s before the string is used for anything (unless the programmer doesn't care about it). Unixes typically use \n as its end-of-line sequence, MS-DOS and Windows uses \r\n, and Mac OSes used \r before OS X.
#include <stdio.h>
int getc(FILE *stream);
The getc function is equivalent to fgetc, except that it may be implemented as a macro. If it is implemented as a macro, the stream argument may be evaluated more than once, so the argument should never be an expression with side effects (i.e. have an assignment, increment, or decrement operators, or be a function call).
The getc function returns the next character from the input stream pointed to by stream. If the stream is at end-of-file, the end-of-file indicator for the stream is set and getc returns EOF (EOF is a negative value defined in <stdio.h>, usually (-1)). If a read error occurs, the error indicator for the stream is set and getc returns EOF.
#include <stdio.h>
int getchar(void);
The getchar function is equivalent to getc with the argument stdin.
The getchar function returns the next character from the input stream pointed to by stdin. If stdin is at end-of-file, the end-of-file indicator for stdin is set and getchar returns EOF (EOF is a negative value defined in <stdio.h>, usually (-1)). If a read error occurs, the error indicator for stdin is set and getchar returns EOF.
#include <stdio.h>
char *gets(char *s);
The gets function reads characters from the input stream pointed to by stdin into the array pointed to by s until an end-of-file is encountered or a new-line character is read. Any new-line character is discarded, and a null character is written immediately after the last character read into the array.
The gets function returns s if successful. If the end-of-file is encountered and no characters have been read into the array, the contents of the array remain unchanged and a null pointer is returned. If a read error occurs during the operation, the array contents are indeterminate and a null pointer is returned.
This function and description is only included here for completeness. Most C programmers nowadays shy away from using gets, as there is no way for the function to know how big the buffer is that the programmer wants to read into. Commandment #5 of Henry Spencer's The Ten Commandments for C Programmers (Annotated Edition) reads, "Thou shalt check the array bounds of all strings (indeed, all arrays), for surely where thou typest foo someone someday shall type supercalifragilisticexpialidocious." It mentions gets in the annotation: "As demonstrated by the deeds of the Great Worm, a consequence of this commandment is that robust production software should never make use of gets(), for it is truly a tool of the Devil. Thy interfaces should always inform thy servants of the bounds of thy arrays, and servants who spurn such advice or quietly fail to follow it should be dispatched forthwith to the Land Of Rm, where they can do no further harm to thee."
#include <stdio.h>
int ungetc(int c, FILE *stream);
The ungetc function pushes the character specified by c (converted to an unsigned char) back onto the input stream pointed to by stream. The pushed-back characters will be returned by subsequent reads on that stream in the reverse order of their pushing. A successful intervening call (with the stream pointed to by stream) to a file-positioning function (fseek, fsetpos, or rewind) discards any pushed-back characters for the stream. The external storage corresponding to the stream is unchanged.
One character of pushback is guaranteed. If the ungetc function is called too many times on the same stream without an intervening read or file positioning operation on that stream, the operation may fail.
If the value of c equals that of the macro EOF, the operation fails and the input stream is unchanged.
A successful call to the ungetc function clears the end-of-file indicator for the stream. The value of the file position indicator for the stream after reading or discarding all pushed-back characters shall be the same as it was before the characters were pushed back. For a text stream, the value of its file-position indicator after a successful call to the ungetc function is unspecified until all pushed-back characters are read or discarded. For a binary stream, its file position indicator is decremented by each successful call to the ungetc function; if its value was zero before a call, it is indeterminate after the call.
The ungetc function returns the character pushed back after conversion, or EOF if the operation fails.
#include <stdio.h>
size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream);
The fread function reads, into the array pointed to by ptr, up to nmemb elements whose size is specified by size, from the stream pointed to by stream. The file position indicator for the stream (if defined) is advanced by the number of characters successfully read. If an error occurs, the resulting value of the file position indicator for the stream is indeterminate. If a partial element is read, its value is indeterminate.
The fread function returns the number of elements successfully read, which may be less than nmemb if a read error or end-of-file is encountered. If size or nmemb is zero, fread returns zero and the contents of the array and the state of the stream remain unchanged.
All text is available under the terms of the GNU Free Documentation License
Source : Wikibooks
