文件操作知识

#include <stdio.h>
 int main()
 {
 int a = 10000;
 FILE* pf = fopen("test.txt", "wb");
 fwrite(&a, 4, 1, pf);
 fclose(pf);
 pf = NULL;
 return 0;
 }

struct _iobuf {
char *_ptr;
int _cnt;
char *_base;
int _flag;
int _file;
int _charbuf;
int _bufsiz;
char *_tmpfname;
};
typedef struct _iobuf FILE;

FILE* pf;//⽂件指针变量

//打开⽂件
FILE * fopen ( const char * filename, const char * mode );
//关闭⽂件
int fclose ( FILE * stream );

#include <stdio.h>
int main ()
{
FILE * pFile;
pFile = fopen ("myfile.txt","w");
if (pFile!=NULL)
{
fputs ("fopen example",pFile);
fclose (pFile);
}
return 0;
}

#include <stdio.h>
int main()
{
	FILE* pf = fopen("data.txt", "r");
	if (pf == NULL)
	{
		perror("fopen");
		return 1;
	}
     int ch = fgetc(pf);
     printf("%c\n", ch);//a
     ch = fgetc(pf);
     printf("%c\n", ch);//b
     ch = fgetc(pf);
     printf("%c\n", ch);//c
	while ((ch = fgetc(pf)) != EOF)
	{
		printf("%c ", ch);
	}
	fclose(pf);
	pf = NULL;
	return 0;
}
//读取字符成功，返回字符的ASCII的值.如果读取失败或者遇到文件末尾
//设置一个错误状态值-ferror；如果遇到文件末尾，设置一个遇到文件末尾的状态值-feof

#include <stdio.h>
int main()
{
	FILE* pf = fopen("data.txt", "w");
	if (pf == NULL)
	{
		perror("fopen");
		return 1;
	}
	char arr[20] = "hello";
	int num = 100;
	double pai = 3.14;
	fprintf(pf, "%s %d %.2lf", arr, num, pai);	
	fclose(pf);
	pf = NULL;
	return 0;
}

#include <stdio.h>
struct S
{
	char arr[20];
	int num;
	double pai;
};
int main()
{
	FILE* pf = fopen("data.txt", "w");
	if (pf == NULL)
	{
	perror("fopen");
		return 1;
	}
	struct S s = { "world", 200, 3.14 };	
	fprintf(pf, "%s %d %.2lf", s.arr, s.num, s.pai);
	fclose(pf);
	pf = NULL;
    return 0;
}

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

#include <stdio.h>
 int main ()
 {
 FILE * pFile;
 pFile = fopen ( "example.txt" , "wb" );
 fputs ( "This is an apple." , pFile );
 fseek ( pFile , 9 , SEEK_SET );
 fputs ( " sam" , pFile );
 fclose ( pFile );
 return 0;
 }

long int ftell ( FILE * stream );

#include <stdio.h>
 int main ()
 {
 FILE * pFile;
 long size;
 pFile = fopen ("myfile.txt","rb");
 if (pFile==NULL)
 perror ("Error opening file");
 else
 {
 fseek (pFile, 0, SEEK_END); 
 size=ftell (pFile);
 fclose (pFile);
 printf ("Size of myfile.txt: %ld bytes.\n",size);
 }
 return 0;
 }

void rewind ( FILE * stream );

#include <stdio.h>
 int main ()
 {
 int n;
 FILE * pFile;
 char buffer [27];
 pFile = fopen ("myfile.txt","w+");
 for ( n='A' ; n<='Z' ; n++)
 fputc ( n, pFile);
 rewind (pFile);
 fread (buffer,1,26,pFile);
 fclose (pFile);
 buffer[26]='\0';
 printf(buffer);
 return 0;
 }

//⽂本⽂件的例⼦
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
int c; // 注意：int，⾮char，要求处理EOF
FILE* fp = fopen("test.txt", "r");
if(!fp) {
perror("File opening failed");
return EXIT_FAILURE;
}
//fgetc 
while ((c = fgetc(fp)) != EOF) 
{
putchar(c);
}
if (ferror(fp))
puts("I/O error when reading");
else if (feof(fp))
puts("End of file reached successfully");
fclose(fp);
}

 //⼆进制⽂件的例⼦
 #include <stdio.h>
 enum { SIZE = 5 };
 int main(void)
 {
 double a[SIZE] = {1.,2.,3.,4.,5.};
 FILE *fp = fopen("test.bin", "wb");
 fwrite(a, sizeof *a, SIZE, fp); 
 fclose(fp);
 double b[SIZE];
 fp = fopen("test.bin","rb");
 size_t ret_code = fread(b, sizeof *b, SIZE, fp);
 if(ret_code == SIZE) {
 puts("Array read successfully, contents: ");
 for(int n = 0; n < SIZE; ++n)
 printf("%f ", b[n]);
 putchar('\n');
 } else { 
 if (feof(fp))
 printf("Error reading test.bin: unexpected end of file\n");
 else if (ferror(fp)) {
 perror("Error reading test.bin");
 }
 }
 fclose(fp);
 }

 #include <stdio.h>
 #include <windows.h>
 int main()
 {
 FILE*pf = fopen("test.txt", "w");
 fputs("abcdef", pf);//先将代码放在输出缓冲区
 printf("睡眠10秒-已经写数据了，打开test.txt⽂件，发现⽂件没有内容\n");
 Sleep(10000);
 printf("刷新缓冲区\n");
 fflush(pf);//刷新缓冲区时，才将输出缓冲区的数据写到⽂件（磁盘）
 //注：fflush 在⾼版本的VS上不能使⽤了
 printf("再睡眠10秒-此时，再次打开test.txt⽂件，⽂件有内容了\n");
 Sleep(10000);
 fclose(pf);
 //注：fclose在关闭⽂件的时候，也会刷新缓冲区
 pf = NULL;
 return 0;
 }