抽丝剥茧C语言（高阶）文件操作+练习

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 );//第一个参数是打开什么文件，文件如果没有路径，默认路径就是你编译器中你源文件的根目录下，第二个参数是以什么类型的方式打开这个文件
//关闭文件
int fclose ( FILE * stream );//参数是你打开文件的位置

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
	FILE* p = fopen("test.txt", "r");//以只读的方式打开test.txt这个文件
	if (p == NULL)//如果文件不存在就返回空指针
	{
		printf("%s", strerror(errno));//报错
		return 1；
	}
	fclose(p);//关闭文件
	p=NULL;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
	FILE* p = fopen("test.txt", "w");
	if (p == NULL)
	{
		printf("%s", strerror(errno));
		return 1;
	}

	fclose(p);
	p=NULL;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
	FILE* p = fopen("test.txt", "w");
	if (p == NULL)
	{
		printf("%s", strerror(errno));
		return 1;
	}
	fputc('a', p);
	fclose(p);
	p = NULL;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
	FILE* p = fopen("test.txt", "r");
	if (p == NULL)
	{
		printf("%s", strerror(errno));
		return 1;
	}
	/*fputc('a', p);*/
	int e = 0;
	if ((e = fgetc(p)) != EOF)//如果不是EOF就打印
	{
		printf("%c", e);
	}
	fclose(p);
	p = NULL;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
	FILE* p = fopen("test.txt", "w");
	if (p == NULL)
	{
		printf("%s", strerror(errno));
		return 1;
	}
	/*fputc('a', p);*/
	/*int e = 0;
	if ((e = fgetc(p)) != EOF)
	{
		printf("%c", e);
	}*/
	fputs("qweqwe", p);
	fclose(p);
	p = NULL;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
	FILE* p = fopen("test.txt", "r");
	if (p == NULL)
	{
		printf("%s", strerror(errno));
		return 1;
	}
	/*fputc('a', p);*/
	/*int e = 0;
	if ((e = fgetc(p)) != EOF)
	{
		printf("%c", e);
	}*/
	/*fputs("qweqwe", p);*/
	char arr[10] = { 0 };
	fgets(arr, 4, p);
	printf("%s", arr);
	fclose(p);
	p = NULL;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct person
{
	char name[20];
	int age;
	float weight;
};
int main()
{
	struct person s = { "baiye",25,75.0f };
	FILE* p = fopen("test.txt", "w");
	if (p == NULL)
	{
		perror("fopen");
		return 1;
	}
	fprintf(p, "%s %d %f", s.name, s.age, s.weight);

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

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct person
{
	char name[20];
	int age;
	float weight;
};
int main()
{
	struct person s = { 0 };//我们并没有初始化任何值
	FILE* p = fopen("test.txt", "r");
	if (p == NULL)
	{
		perror("fopen");
		return 1;
	}
	//fprintf(p, "%s %d %f", s.name, s.age, s.weight);
	fscanf(p, "%s %d %f", s.name, &(s.age), &(s.weight));
	printf("%s %d %f", s.name, s.age, s.weight);
	fclose(p);
	p = NULL;
	return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct person
{
	char name[20];
	int age;
	float weight;
};
int main()
{
	struct person s = { "baiye",25,75.00 };
	FILE* p = fopen("test.txt", "wb");
	if (p == NULL)
	{
		perror("fopen");
		return 1;
	}
	fwrite(&s, sizeof(struct person), 1, p);
	fclose(p);
	p = NULL;
	return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct person
{
	char name[20];
	int age;
	float weight;
};
int main()
{
	struct person s = { 0 };
	FILE* p = fopen("test.txt", "rb");
	if (p == NULL)
	{
		perror("fopen");
		return 1;
	}
	//fwrite(&s, sizeof(struct person), 1, p);
	fread(&s, sizeof(struct person), 1, p);
	printf("%s %d %f", s.name, s.age, s.weight);
	fclose(p);
	p = NULL;
	return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct person
{
	char name[20];
	int age;
	float weight;
};
int main()
{
	struct person s = { "baiye",25,75.00 };
	char arr[100] = { 0 };
	sprintf(arr, "%s %d %f", s.name, s.age, s.weight);
	printf("%s", arr);//原理是让结构体里面的数据变成了这样子"baiye 25 75.00"
	return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct person
{
	char name[20];
	int age;
	float weight;
};
int main()
{
	struct person s = { "baiye",25,75.00 };
	struct person s1 = { 0 };
	char arr[100] = { 0 };
	sprintf(arr, "%s %d %f", s.name, s.age, s.weight);
	printf("字符串：%s\n", arr);//原理是让结构体里面的数据变成了这样子"baiye 25 75.00"
	sscanf(arr, "%s %d %f", s.name, &(s.age), &(s.weight));
	printf("格式化：%s %d %f\n", s.name, s.age, s.weight);
	return 0;
}

#include <stdio.h>
int main()
{
	FILE* pFile;
	pFile = fopen("example.txt", "rb");
	//fputs("This is an apple.", pFile);
	fseek(pFile, 9, SEEK_SET);
	int i = fgetc(pFile);
	printf("%c\n", i);
	fseek(pFile, 2, SEEK_CUR);
	i = fgetc(pFile);
	printf("%c\n", i);
	fseek(pFile, -2, SEEK_END);
	i = fgetc(pFile);
	printf("%c\n", i);
	fclose(pFile);
	pFile = NULL;
	return 0;
}

#include <stdio.h>
int main()
{
	FILE* pFile;
	pFile = fopen("example.txt", "rb");
	//fputs("This is an apple.", pFile);
	fseek(pFile, 9, SEEK_SET);
	int i = fgetc(pFile);
	printf("%c\n", i);
	printf("%d\n", ftell(pFile));//打印偏移量的位置
	fseek(pFile, 2, SEEK_CUR);
	i = fgetc(pFile);
	printf("%c\n", i);
	printf("%d\n", ftell(pFile));
	fseek(pFile, -2, SEEK_END);
	i = fgetc(pFile);
	printf("%c\n", i);
	printf("%d\n", ftell(pFile));
	fclose(pFile);
	pFile = NULL;
	return 0;
}

#include <stdio.h>
int main()
{
	FILE* pFile;
	pFile = fopen("example.txt", "rb");
	//fputs("This is an apple.", pFile);
	fseek(pFile, 9, SEEK_SET);
	int i = fgetc(pFile);
	printf("%c\n", i);
	printf("%d\n", ftell(pFile));
	fseek(pFile, 2, SEEK_CUR);
	i = fgetc(pFile);
	printf("%c\n", i);
	printf("%d\n", ftell(pFile));
	fseek(pFile, -2, SEEK_END);
	i = fgetc(pFile);
	printf("%c\n", i);
	printf("%d\n", ftell(pFile));
	rewind(pFile);//让指针回到起始位置
	i = fgetc(pFile);
	printf("%c\n", i);
	printf("%d\n", ftell(pFile));
	fclose(pFile);
	pFile = NULL;
	return 0;
}

#include <stdio.h>
int main()
{
	int a = 10000;
	FILE* pf = fopen("test.txt", "wb");
	fwrite(&a, 4, 1, pf);//二进制的形式写到文件中
	fclose(pf);
	pf = NULL;
	return 0;
}

#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 当读取失败的时候或者遇到文件结束的时候，都会返回EOF
	while ((c = fgetc(fp)) != EOF) // 标准C I/O读取文件循环
	{
		putchar(c);
	}
	//判断是什么原因结束的
	if (ferror(fp))//判断是不是遇到文件错误了
		puts("I/O error when reading");//文件读取失败
	else if (feof(fp))
		puts("End of file reached successfully");//文件读取到末尾
	fclose(fp);
}

#include <stdio.h>
#include <stdlib.h>
enum { SIZE = 5 };
int main(void) {
	double a[SIZE] = { 1.,2.,3.,4.,5. };
	FILE* fp = fopen("test.bin", "wb"); // 必须用二进制模式
	fwrite(a, sizeof * a, SIZE, fp); // 写 double 的数组
	fclose(fp);
	double b[SIZE];
	fp = fopen("test.bin", "rb");
	size_t ret_code = fread(b, sizeof * b, SIZE, fp); // 读 double 的数组
	if (ret_code == SIZE) //说明读到了5个元素
	{
		puts("Array read successfully, contents: ");
		for (int n = 0; n < SIZE; ++n) printf("%f ", b[n]);
		putchar('\n');
	}
	else // error handling
	{ 
		if (feof(fp))//看看是否是读到了文件末尾
			printf("Error reading test.bin: unexpected end of file\n");
		else if (ferror(fp)) //看看文件是否出错了
		{
			perror("Error reading test.bin");
		}
	}
	fclose(fp);
}

#include <stdio.h>
#include <windows.h>
//VS2013 WIN10环境测试
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;
}