Prototypes and notes of C standard file io functions

 fopen()

Requires header file: #include

Function prototype: FILE *fopen(const char *path,const char *mode)

Function parameters: path: the path and file name of the file to be opened

mode: file opening method, see below

Function return value: Success: FILE type pointer pointing to the file

Failure: NULL

The following are the allowed values ​​and descriptions of the mode parameter:

r or rb opens the file in read-only mode. The file must exist

r+ or r+b opens the file in a readable and writable manner. The file must exist

w or wb opens the file in write-only mode. If the file does not exist, it is created; if the file exists, the original content of the file is erased and the file is operated from the beginning.

w+ or w+b opens the file in a readable and writable manner. If the file does not exist, it is created; if the file exists, the original content of the file is erased and the file is operated from the beginning.

a or ab opens a write-only file in append mode. If the file does not exist, it is created; if the file exists, the written data is appended to the end of the file, that is, the original content of the file will be retained.

a+ or a+b opens a readable and writable file in append mode. If the file does not exist, it is created; if the file exists, the written data is appended to the end of the file, that is, the original content of the file will be retained.

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gets(), fgets()

Requires header file: #include

Function prototype: char *gets(char *s)

char *fgets(char *s,int size,FILE *stream)

Function:

Assume that the length of buff is MAX; then there are two ways to stop fgetc:

1. When reading /n, write the ascii of /n into buff and stop, and add a '\0' at the end;

2. When size-1 characters are read but no /n is read, the sequence ends and a '\0' is added at the end;

Function parameters: s: buffer address where input characters are stored

size: the length of the input string

stream: input file stream

Function return value:

Success:s

Failure or end of file: NULL

puts(), fputs()

Requires header file: #include

Function prototype: int puts(const char *s)

int fputs(const char *s,FILE *stream)

Function parameters: s: buffer address where output characters are stored

stream: output file stream

Function return value: Success: non-negative number

Failure: EOF

scanf(), fscanf(), sscanf()

Requires header file: #include

Function prototype: int scanf(const char *format,...);

int fscnaf(FILE *fp,const char *format,...);

int sscanf(char *buf,const char *format,...);

Function parameters: format: input format

fp: stream to be input

buf: buffer to be input

Function return value: Success: the number of data read

Failure: EOF

printf(), fprintf(), sprintf()

Requires header file: #include

Function prototype: int printf(const char *format,...);

int fprintf(FILE *fp,const char *format,...);

int sprintf(char *buf,const char *format,...);

Function parameters: format: output format

fp: stream to be output

buf: buffer to be output

Function return value: Success: Number of characters output

Failure: EOF

fread()

Requires header file: #include

Function prototype: size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream);

Function parameters: ptr: buffer for storing read data

size: The size of each data item read (in bytes)

nmemb: number of data read

stream: the stream to read

Function return value:

Success: The actual number of nmemb read

Failure: 0

fwrite()

Requires header file: #include

Function prototype: size_t fwrite(void *ptr,size_t size,size_t nmemb,FILE *stream);

Function parameters: ptr: buffer to store written data

size: The size of each data item written (in bytes)

nmemb: Number of data written

stream: the stream to write to

Function return value: Success: The actual number of nmemb written

Failure: 0

The feof()/ferror() functions can be used to determine whether the read operation is wrong or the file has been read to the end.

When opening a stream, the offset is 0 (the beginning of the file).

fseek()

Requires header file: #include

Function prototype: int fseek(FILE *stream, long offset, int whence);

Function parameters: stream: the stream to be positioned

offset: offset relative to the reference point whence

whence: reference point (values ​​see below)

Function return value: Success: 0, change the read and write position

Failure: EOF, no change in read or write position

The value of the third parameter whence is as follows:

SEEK_SET: represents the starting position of the file, the number is 0

SEEK_CUR: represents the current read and write position of the file, the number is 1

SEE

K_END: ​​represents the end position of the file, the number is 2

Function ftell()

Requires header file: #include

Function prototype: int ftell(FILE *stream);

Function parameters: stream: the stream to be positioned

Function return value: Success: Returns the current read and write position

Failure: EOF