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This article introduces the knowledge of "what is the sequential reading and writing function of C language files". In the operation of actual cases, many people will encounter such a dilemma. Next, let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

First, the sequential read and write functions fgetc and fputc of files

Fgetc

The character input function applies to all input streams

Fputc

The character output function applies to all output streams

Int fgetc (FILE * stream); int fputc (int c, FILE * stream)

Fputc writes files

Int main () {FILE* pfWrite = fopen ("test.txt", "w"); if (pfWrite = = NULL) / / verify {printf ("% s\ n", strerror (errno)); / / if write file error printing error reason return 0;} / write file fputc ("a", pfWrite) Fputc ("b", pfWrite); fputc ("c", pfWrite); / / close the file fclose (pfWrite); pfWrite = = NULL; return 0;}

Fgetc reads the file

Int main () {FILE* pfRead = fopen ("test.txt", "r"); if (pfRead = = NULL) {printf ("% s\ n", strerror (errno)); return 0;} / read file printf ("% s", fgetc (pfRead)); / / a printf ("% s", fgetc (pfRead)) / b printf ("% s", fgetc (pfRead)); / / c / / close the file fclose (pfRead); pfRead = = NULL; return 0;} fgets and fputs

The fges text line input function applies to all input streams

The fputs text line input function applies to all output streams

The functions of the two functions:

/ / Get a string from a stream. Gets a string from the stream. Char * fgets (char * string, int n, FILE * stream); / / Write a string to a stream. Writes a string to the stream. Int fputs (const char * string, FILE * stream)

Read a line with the fgets function:

Int main () {char buff [100] = {0}; FILE* pf = fopen ("test.txt", "r"); if (pf = = NULL) {return 0;} / read file fgets (buff, 100, pf); printf ("% s", buff) / / notice that there is a newline character in buff (there is a newline character at the end of the file) / / opened successfully, read the file, and close the file fclose (pf); pf = = NULL; return 0;}

Read a line and print it to the monitor as shown in the picture:

Write a line with the fputs function:

Int main () {char buff [100] = {0}; FILE* pf = fopen ("test.txt", "w"); if (pf = = NULL) {return 0;} / / write file fputs ("hello\ n", pf); fputs ("word\ n", pf) / / Open successfully, write the file, close the file fclose (pf); pf = NULL; return 0;}

Write a line to the file with fputs: as follows:

Fgets and fputs can also operate keyboards and screens

Keyboard input abcd enter screen print abcd

Fscanf and fprintf

The fscanf formatting input function applies to all input streams

The fprintf formatted output function applies to all output streams

Simple comparison of scanf and fscanf,printf and fprintf, the usage is very similar

Int scanf (const char * format [, argument]... Int fscanf (FILE * stream, const char * format [, argument]... Int printf (const char * format [, argument]... ); int fprintf (FILE * stream, const char * format [, argument]...)

Fprintf writes files

Struct S {int n; float score; char arr [10];}; int main () {struct S s = {100,3.14, "abc"}; FILE* pf = fopen ("test.txt", "w"); if (pf = = NULL) {return 0 } / / formatted file fprintf (pf, "d% f% s", s.n, s.score, s.arr); fclose (pf); pf = NULL; return 0;}

Fscanf reads the file

Struct S {int n; float score; char arr [10];}; int main () {struct S s = {100,3.14, "abc"}; FILE* pf = fopen ("test.txt", "w"); if (pf = = NULL) {return 0 } / / formatted input data fscanf (pf, "d% f% s", s.n, s.score, s.arr); fclose (pf); pf = NULL; return 0;}

Of course, fscanf and fprintf functions can also be applied to standard input / output streams (stdin,stdout).

Compare a set of functions

Scanf/fscanf/sscanf

Ptintf/fprintf/sprintf

Scanf/printf: is a formatted input / output statement for standard input streams / standard output streams

Fscnaf/fprintf: is a formatted input / output statement for all input / output streams

Sscanf/sprintf:sscanf reads formatted data from a string. Sprintf is to output formatted data to (store to) strings

Fraed and fwriite

Fread binary input function applies to files

Fwrite binary output function applies to files

Size_t fwrite (const void * buffer, size_t size, size_t count, FILE* stream); size_t fread (void * buffer, size_t size, size_t count, FILE* stream); struct S {char name [20]; int age; double score;}; int main () {struct S s = {"Zhang San", 2055.6}; FILE* pf = fopen ("test.txt", "wb") If (pf = = NULL) {return 0;} / / binary file fwrite (& s, sizeof (struct S), 1, pf); fclose (pf); pf = NULL; return 0;}

Fread reads the file and fwrite writes the file. The usage of the two functions is similar

Second, the random read-write function of the file

The functions described above are all sequential read-write functions, and sometimes we need to start reading and writing functions from a certain location. The following functions perform their functions.

Fseek function

Locate the file pointer according to its location and offset

Moves the file pointer to a specified location.int fseek (FILE* stream, long offset, int origin); / / what the three parameters refer to: the current position of the pf offset file pointer int main () {FILE* pf = fopen ("test.txt", "r"); if (pf = = NULL) {return 0 } / / locate the file pointer fseek (pf,2,SEEK_CUR); / / offset is 2 / / read the file int ch = fgetc (pf); prinf ("% c\ n", ch); fclose (pf); pf = NULL; return 0;}

As shown in the figure, the offset is 2 from the current position an of the file pointer, and print c

SEEK_CUR

Current position of file pointer (current location of the file pointer)

SEEK_END (location at the end of the file)

End of file

SEEK_SET (file start location)

Beginning of file

III. Judgment on the end of the document

We know: EOF-- > the flag for the end of the end of file file

If there is nothing in a file, what we open the file to read is "- 1", and there is an EOF at the end of the file.

Feof function

Keep in mind that during the file reading process, the return value of the feof function cannot be used to determine whether the file is finished or not.

Instead, it is used to determine whether the read fails to end when the file is finished, or when the tail EOF is encountered to end the file.

Whether the text file is finished reading, and determine whether the return value is EOF or NULL

For example, fgetc determines whether it is EOF fgets and whether the return value is NULL.

Judge the end of reading the binary file and determine whether the return value is less than the actual number to be read.

For example, fread determines whether the returned value is less than the actual number to be read.

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