Basic knowledge of documents

Knowledge about documents

Classification of documents

1. Program files ： image .c Source file for suffix ,.obj Target file for suffix ,.exe Executable program with suffix .
2. Data files ： Data when the program reads and writes .

Or according to another classification

The documents are divided into ：1. text file .2. Binary .

Data is stored in binary form in memory , Output directly to external memory without conversion , Binary files ; If conversion is added , With ASCII Standard storage is text files .

Data files

file name ： The unique identification of a file .

Include ： File path , File name trunk , file extension

Opening and closing of files

1. The file pointer

The file pointer is actually a structure variable name FILE, The members inside are used to store the relevant information of the file . These information together constitute the file information area of each different file .

Every time you open a file , The system will create different FILE, adopt FILE* Create a variable pf, there pf It's a file pointer , It can point to the corresponding file .

2. Opening and closing of documents

Before reading and writing files , The file should be opened ; When the relevant operation is over , The file should be closed .

The standard specifies the use of fopen To open the file , use fclose To close the file .

fopen

FILE* fopen(const char* filename, const char* mode);

When the file is successfully opened , What is returned is a pointer to the structure of a specific file information area ; Open failure returns a null pointer , therefore , When using files , We have to judge .

How to open some important files

How to open the file	Specific meaning	file does not exist
“r”	To input data, open the file	Report errors
“w”	To output data, open a file	Create a new file
“rb”	To enter data , Open a binary file	Report errors
“wb”	To output data , Open a binary file	Create a new file

fclose

int fclose(FILE* stream);

give an example

#include <stdio.h>
#include <string.h>
#include <errno.h>

int main()
{
    
    FILE* pf = fopen("test.txt", "w");
    if (pf == NULL)
    {
    
        printf("%s\n", strerror(errno));
        return;
    }
    // Document related operations 
    //...
    fclose(pf);
    
    return 0;
}

Sequential reading and writing of files

function	Function name	Using range
Character input	fgetc	All input streams
Character output	fputc	All input streams
Text input	fgets	All input streams
Text output	fputs	All input streams
Format input	fscanf	All input streams
Format output	fprintf	All input streams
Binary input	fread	file
Binary output	fwrite	file

Random reading and writing of documents

fseek

int fseek(FILE* stream, long offset, int origin);

This function is 3 Parameters , The first is a file pointer , The second is the offset , The third is the starting position .

If the starting position is the first element, it is 0, The last element is -1.

Through this 3 Parameters can be located to the relevant location of the file , Read and write .

ftell

long ftell(FILE* stream);

If the function returns normally , Returns the offset of the file pointer from the starting position .

rewind

void rewind(FILE* stream);

Let the file pointer point to the starting position of the file .

Judgment of the end of file reading

feof

int feof(FILE* stream);

This function is used to end the file , Judge whether the reading fails or the end of the file is encountered .

1. Judge whether the reading of the text file is over ：

fgetc Judge whether it is EOF

fgets Judge whether it is NULL

2. Judge whether the reading of binary file is over

Judge whether the return value is less than the actual number to be read ,fread Judge whether the return value is less than the actual number to be read .