Close file

fclose(fp)；

fp=NULL；

Open file

FILE* fp=fopen("xxx.xxx","xx");

The first parameter is the type of file set

The second parameter has the following

operation	effect	file does not exist
"w" (write only)	To output data, open a text file	Create a new file
"r" (read only)	To output data, open an existing file	error
"a" (added)	Add data to the end of a text file	error
"rb" (read only)	To enter data, open a binary file	error
"wb" (write only)	To output data, open a binary file	Create a new file
"ab" (additional)	Add data to the end of a binary file	error
"r +" (read / write)	To read and write, open a text file	error
"w +" (read / write)	Create a new file for reading and writing	Create a new file
"a +" (read / write)	Open a file and read and write at the end of the file	Create a new file
"rb +" (read / write)	To read and write, open a binary file	error
"wb +" (sketch)	To read and write, create a new text file	Create a new file
"ab +" (read / write)	Open a binary file and read and write at the end of the file	Create a new file

The functions related to sequential file reading and writing are

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

Keyboard -- standard input device ----- stdin

Screen -- standard output device ----- stdout

Use of fputc function

int main()
{
	FILE* fpwrite = fopen("text.txt", "w");
	if (fpwrite == NULL)
	{
		perror("Open failed");
		return;
	}
	fputc('H', fpwrite);
	fputc('e', fpwrite);
	fputc('l', fpwrite);
	fputc('l', fpwrite);
	fputc('o', fpwrite);


	fclose(fpwrite);
	fpwrite = NULL;

	return 0;
}

After running, you can see in the text.txt file

  Use of fgetc function

text.txt contains Hello

int main()
{
	FILE* fpread = fopen("text.txt", "r");
	if (fpread == NULL)
	{
		perror("Open failed");
		return;
	}
	printf("%c\n", fgetc(fpread));
	printf("%c\n", fgetc(fpread));
	printf("%c\n", fgetc(fpread));
	printf("%c\n", fgetc(fpread));
	printf("%c\n", fgetc(fpread));


	fclose(fpread);
	fpread = NULL;

	return 0;
}

After running, you can see it on the command console

Use of fputs function

int main()
{
	FILE* fpwrites = fopen("text1.txt", "w");
	if (fpwrites == NULL)
	{
		perror("Open failed");
		return;
	}
	fputs("Hello", fpwrites);
	fputs("World", fpwrites);

	fclose(fpwrites);
	fpwrites = NULL;
	return 0;
}

  Display in text1.txt file

Use of fgets function

int main()
{
	FILE* fpreads = fopen("text1.txt", "r");
	char tmp[100] = { 0 };
	if (fpreads == NULL)
	{
		perror("Open failed");
		return;
	}
	//Output 50 characters from fpreads to tmp
	fgets(tmp, 50, fpreads);
	//Output tmp
	printf("%s\n", tmp);
	fclose(fpreads);
	fpreads = NULL;
	return 0;
}

  Display in command desk

The fprintf function uses

int main()
{
	FILE* fpwrite = fopen("text2.txt", "w");
	if (fpwrite == NULL)
	{
		perror("Open failed");
		return;
	}

	fprintf(fpwrite, "%s %s %s %d", "Hello", "Word", "in", 2021);

	fclose(fpwrite);
	fpwrite = NULL;
	return 0;
}

  Display in text2.txt

  Use of fscanf function

int main()
{
	FILE* fpread = fopen("text2.txt", "r");
	char arr1[20] = { 0 };
	char arr2[20] = { 0 };
	char arr3[20] = { 0 };
	int year = 0;
	if (fpread == NULL)
	{
		perror("Open failed");
		return;
	}
	//Store the data in fpread in Arr1, arr2, arr3 and year
	fscanf(fpread, "%s %s %s %d", arr1, arr2, arr3, &year);
	printf("%s %s %s %d", arr1, arr2, arr3, year);
	fclose(fpread);
	fpread = NULL;
	return 0;
}

Display on command console

fwrit function uses

int main()
{
	int a = 10000;
	FILE* fpwrite = fopen("text3.txt", "wb");
	if (fpwrite == NULL)
	{
		perror("Open failed");
		return;
	}
	//Store a element in four bytes in fpwrite
	fwrite(&a, 4, 1, fpwrite);//Write to file in binary mode
	fclose(fpwrite);
	fpwrite = NULL;
	return 0;
}

  Open text3.txt in a binary editor

Using the fread function

int main()
{
	FILE* fpread = fopen("text3.txt", "rb");
	int a = 0;

	if (fpread == NULL)
	{
		perror("Open failed");
		return;
	}
	/* Read and display data */
	fread(&a, sizeof(a), 1, fpread);
	printf("%d\n", a);
	fclose(fpread);
	fpread = NULL;
	return(0);
}

  Display on command console