C language files and special modifiers

Static and extern:

static modifier variable (can be decorated with local variables), only the source code file containing that variable definition can be accessed (internal variables)

Extends the life cycle of local variables, from program initiation to exit

Function: variable scope defined by static is extended

Static statements that define variables are only executed once

extern-defined variables which source files can be used as long as they are declared (external variables)

extern can not modify local variables

The effect of static on global variables

Static modified global variables can only be used in the current file, not in other files

The static modifier is an intrinsic function (it can only be used in a defined file)

extern-modified functions can be used both internally and externally (can be declared in a header file or before use)

12) file Operation:

The fopen function is used to open a file in the general form:

File pointer variable name = fopen (filename, file usage)

FILE *FP = NULL;

fp = fopen ("A.txt", "R"); Open a file as read-only

if (fp! = NULL) {

Manipulating files

}else{

Prompt user

}

Fclose (FP);

Gracefully closes the file fclose returns 0, and if other returns, the shutdown error occurs. Failure to write file if not closed

File operation steps:

1) Create a file pointer

FILE *FP = NULL;

2) Open File

fopen (file name, operation mode);

If the opening succeeds, returns the first address of the file, and fails to return null;

character read and write functions:

FPUTC (character amount, file pointer);//The amount of characters to write can be a character constant or a variable

FPUTC (' A ', FP);

Cases:

char ch = ' X ';

FILE *FP = NULL;

fp = fopen ("Fputs.txt", "w");

if (fp! = NULL) {

FPUTC (CH, FP);

printf ("Write success");

ch = fget (FP);

}

Fclose (FP);

char s = fgetc (FP);

while (s! = EOF) {//eof file at the end of the flag

Putchar (s);

s = fgetc (FP); The system automatically reads the next character

}

Char ch;

FILE *FP = fopen ("InputString.txt", "w+");

if (fp = NULL) {

printf ("Please enter string:");

ch = getchar ();

int count = 0;

while (ch! = ' \ n ') {

count++;

FPUTC (CH, FP);

ch = getchar ();

}

printf ("entered altogether%d characters \ n", count);

Rewind (FP); Point the file pointer back to the file header

ch = fgetc (FP);

while (ch! = EOF) {

Putchar (CH);

ch = fgetc (FP);

}

Fclose (FP);

return 0;

}

Count = fputs (str, FP);//count returns the length of this write string

Char str[50]; Fgets read, when the contents of the file is read, it will automatically add the

Fget (str, sizeof (STR), FP); Fgets read, reading ends when read to \ n or EOF

Char *s = "ASDFASD";

Fputs (S, FP);

Char str[3];//length is 3, one man reads half, length is 4 read all

Fgets (str, sizeof (STR), FP);

Fread (buffer, size, count, FP)

fwrite (buffer, size, count, FP)

Buffer: Represents the first address that holds the input and output data.

Size: The number of bytes representing the block of data

Count: Indicates the number of blocks of data to read and write

FP: Represents a file pointer

int a= 1, b = 2;

fprintf (FP, "%d#%d;", A, b);

FSCANF (FP, "%d,%d", &arr[i][0], &arr[i][1]);

struct struct Stu;

fseek (file pointer, displacement amount, starting point)

Pointer positioning:

Fseek (FP, sizeof (struct Student), seek_set); Seek_set file First

To read information from a file:

Freak (&str, sizeof (struct Student), 1, FP);

C language files and special modifiers