Common file operations

Catalog

（ One ） Opening and closing of files

（ Two ） Common file operation functions

        （1）fgetc and fputc

          （2）fgets and fputs

        （3）fscanf and fprintf

        （4）fread and fwrite

（ 3、 ... and ） Determination of the end of file reading

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（ One ） Opening and closing of files

         The file should be opened before reading and writing , The file should be closed after use .
         In programming , While opening the file , Will return to one FILE* A pointer variable to the file , It is also equivalent to establishing the relationship between pointer and file .ANSIC To prescribe the use of fopen Function to open a file ,fclose To close the file .

        Open file ：

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

        Close file ：

int fclose ( FILE * stream );

example ：

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
int main()
{
	// Open file 
	FILE* fp = fopen("test.txt", "r");    // Open the file as read 

	// Close file 
	fclose(fp);
	return 0;
}

File opening mode type supplement ：

How files are used	meaning	If the specified file does not exist
"r"	input data , Open an existing text file	error
"w"	Output is data , Open a text file	Create a new file
"a"	Add data to the end of the text file	Create a new file
"rb"	input data , Open a binary file	error
"wb"	Output data , Open a binary file	Create a new file
"ab"	Add data to a binary to the end of the file	error
"r+"	For reading and writing , Open a text file	error
"w+"	For reading and writing , Create a new file	Create a new file
"a+"	Open a file , Then read and write at the end of the file	Create a new file
"rb+"	Open a binary file for reading and writing	error
"wb+"	For reading and writing , Create a new binary	Create a new file
"ab+"	Open a binary file , Read and write for tail	Create a new file

（ Two ） Common file operation functions

        （1）fgetc and fputc

        fgetc：

int fgetc ( FILE * stream );

     fputc：

int fputc ( int character, FILE * stream );

    example ：

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
int main()
{
	// Output 
	FILE* fout = fopen("test.txt", "w");
	// Judge 
	if (fout == NULL)
	{
		perror("Error opening file");
		return 0;
	}
	fputc('A', fout);
	fclose(fout);


	// Input 
	FILE* fin = fopen("test.txt", "r");
	// Judge 
	if (fin == NULL)
	{
		perror("Error opening file");
		return 0;
	}
	char c = fgetc(fin);
	printf("%c", c);
	fclose(fin);

	return 0;
}

 

          （2）fgets and fputs

       fgets

char * fgets ( char * str, int num, FILE * stream );

        fputs

int fputs ( const char * str, FILE * stream );

example ：

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
int main()
{
	// Output 
	FILE* fout = fopen("test.txt", "w");
	// Judge 
	if (fout == NULL)
	{
		perror("Error opening file");
		return 0;
	}
	char arr1[] = "abcdefgh";
	fputs(arr1, fout);
	fclose(fout);


	// Input 
	FILE* fin = fopen("test.txt", "r");
	// Judge 
	if (fin == NULL)
	{
		perror("Error opening file");
		return 0;
	}
	char arr2[10];
	fgets(arr2, 5, fin);
	printf("%s", arr2);
	fclose(fin);

	return 0;
}

        （3）fscanf and fprintf

       fscanf

int fscanf ( FILE * stream, const char * format, ... );

      fprintf

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

example ：

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
struct S
{
	int a;
	int b;
	char c;
};
int main()
{
	struct S s = { 1,15,'T' };
	struct S x;
	// Output 
	FILE* fout = fopen("test.txt", "w");
	// Judge 
	if (fout == NULL)
	{
		perror("Error opening file");
		return 0;
	}
	fprintf(fout, "%d %d %c", s.a, s.b, s.c);
	fclose(fout);


	// Input 
	FILE* fin = fopen("test.txt", "r");
	// Judge 
	if (fin == NULL)
	{
		perror("Error opening file");
		return 0;
	}
	fscanf(fin, "%d %d %c", &x.a, &x.b, &x.c);
	printf("%d %d %c", x.a, x.b, x.c);
	fclose(fin);

	return 0;
}

        （4）fread and fwrite

        fread：

size_t fread ( void * ptr, size_t size, size_t count, FILE * stream );

        fwrite：

size_t fwrite ( const void * ptr, size_t size, size_t count, FILE * stream );

example ：

	#define _CRT_SECURE_NO_WARNINGS
	#include <stdio.h>
	struct S
	{
		int a;
		int b;
		char c;
	};
	int main()
	{
		struct S s = { 2,16,'M' };
		struct S x;
		// Output 
		FILE* fout = fopen("test.txt", "w");
		// Judge 
		if (fout == NULL)
		{
			perror("Error opening file");
			return 0;
		}
		fwrite(&s, sizeof(struct S), 1, fout);
		fclose(fout);


		// Input 
		FILE* fin = fopen("test.txt", "r");
		// Judge 
		if (fin == NULL)
		{
			perror("Error opening file");
			return 0;
		}
		fread(&x, sizeof(struct S), 1, fin);
		printf("%d %d %c", x.a, x.b, x.c);
		fclose(fin);

		return 0;
	}

（ 3、 ... and ） Determination of the end of file reading

         Whether the reading of text file is finished , Determine whether the return value is EOF （ fgetc ）, perhaps NULL （ fgets ）

• fgetc Judge whether it is EOF
• fgets Determine whether the return value is NULL
• fread Judge whether the return value is less than the actual number to be read