C-文件读写相关

1、fputc and fgetc: 按顺序单个读写

int main()
{
	// 绝对路径
	// file* pf = fopen("c:\\users\\fami7z\\source\\repos\\文件学习\\test.txt", "r");
	// 相对路径
	FILE* pf = fopen("test.txt", "r");
	if (pf == NULL)
	{
		perror("fopen");
		return 1;
	}
	// write into file:
	fputc('f', pf);
	fputc('a', pf);
	fputc('m', pf);
	fputc('i', pf);
	// read from file:
	int ret = fgetc(pf);
	printf("%c ", ret);
	ret = fgetc(pf);
	printf("%c ", ret);
	ret = fgetc(pf);
	printf("%c ", ret);
	ret = fgetc(pf);
	printf("%c ", ret);
	ret = fgetc(pf);
	printf("%c ", ret);
	// 从标准输入流按顺序读入数据
	int retfromkeyboard = fgetc(stdin);
	printf("%c ", retfromkeyboard);
	retfromkeyboard = fgetc(stdin);
	printf("%c ", retfromkeyboard);
	retfromkeyboard = fgetc(stdin);
	printf("%c ", retfromkeyboard);
	retfromkeyboard = fgetc(stdin);
	printf("%c ", retfromkeyboard);
	retfromkeyboard = fgetc(stdin);
	printf("%c ", retfromkeyboard);
	// close
	fclose(pf);
	pf = NULL;
	return 0;
}

2、fputs and fgets : 按顺序读写一行数据

int main()
{
	FILE* pf = fopen("text1.txt", "r");
	if (pf == NULL)
	{
		perror("fopen");
		return 1;
	}
	// 按行写入数据
	//fputs("fami\n", pf);
	//fputs("wakatipu\n", pf);

	// 按行读取数据
	char arr1[5] = { 0 };
	char arr2[5] = { 0 };
	fgets(arr1, 5, pf);
	printf("%s\n", arr1);
	fgets(arr2, 5, pf);    // 此行读取的是 "\n"
	printf("%s\n", arr2);
	fgets(arr2, 5, pf);
	printf("%s\n", arr2);
	// 关闭
	fclose(pf);
	pf = NULL;

	return 0;
}

3、fprintf and fscanf : 按顺序按格式读写文件

int main()
{
	struct s stu = { "fami",23,"2021202120" };
	FILE* pf = fopen("按格式读写.txt", "w");
	if (pf == NULL)
	{
		perror("fopen");
		return 1;
	}
	// 按格式写入数据
	fprintf(pf, "%s  %d  %s", stu.name, stu.age, stu.id);

	// 关闭
	fclose(pf);
	pf = NULL;

	return 0;
}

int main()
{
	struct s stu = { 0 };
	FILE* pf = fopen("按格式读写.txt", "r");
	if (pf == NULL)
	{
		perror("fopen");
		return 1;
	}
	// 按格式读数据
	fscanf(pf, "%s  %d  %s", stu.name, &stu.age, stu.id);
	fputs("file contents:\n",stdout);
	//printf("%s  %d  %s\n", stu.name, stu.age, stu.id);
	fprintf(stdout, "%s  %d  %s\n", stu.name, stu.age, stu.id);

	// 关闭
	fclose(pf);
	pf = NULL;

	return 0;
}

4、fread and fwrite : 按顺序按二进制读写文件

struct s
{
	char name[10];
	int age;
	char id[20];
};

int main()
{
	struct s stu[2] = { {"fami",23,"2021202120" },{"waka",24,"2017201720"}};
	FILE* pf = fopen("按二进制读写.txt", "w");
	if (pf == NULL)
	{
		perror("fopen");
		return 1;
	}
	// 按二进制写入数据
	fwrite(&stu, sizeof(struct s), 2, pf);

	// 关闭
	fclose(pf);
	pf = NULL;

	return 0;
}

// attention: 二进制读写时，以文本格式打开，字符的显示不是乱码
int main()
{
	struct s stu[2] = { 0 };
	FILE* pf = fopen("按二进制读写.txt", "r");
	if (pf == NULL)
	{
		perror("fopen");
		return 1;
	}
	// 按二进制读数据
	fread(&stu, sizeof(struct s), 2, pf);
	fputs("file contents:\n", stdout);
	fprintf(stdout, "%s  %d  %s\n", stu[0].name, stu[0].age, stu[0].id);
	fprintf(stdout, "%s  %d  %s\n", stu[1].name, stu[1].age, stu[1].id);

	// 关闭
	fclose(pf);
	pf = NULL;

	return 0;
}

5、fseek (SEEK_CUR/SEEK_END/SEEK_SET)  rewind: 随机读写文件

int main()
{
	FILE* pf = fopen("new.txt", "r");
	if (pf == NULL)
	{
		perror("fopen");
		return 1;
	}
	// read 读一个数据后，SEEK_POS 自动加 1
	int ch = fgetc(pf);
	printf("%c\n", ch);
	// offset = 2
	fseek(pf, 2, SEEK_CUR);
	ch = fgetc(pf);
	printf("%c\n", ch);
	fseek(pf, 1, SEEK_CUR);
	ch = fgetc(pf);
	printf("%c\n", ch);

	rewind(pf);   // 回到起始位置
	ch = fgetc(pf);
	printf("%c\n", ch);
	fseek(pf, -1, SEEK_END);
	ch = fgetc(pf);
	printf("%c\n", ch);

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

6、ferror and feof : feof 不能用于判断文件是否读到末尾处

// 将source.txt的内容拷贝到dest.txt
int main()
{
	FILE* pfread = fopen("source.txt", "r");
	if (!pfread)
	{
		perror("fopen->pfread");
		return 1;
	}
	FILE* pfwrite = fopen("dest.txt", "w");
	if (!pfwrite)
	{
		fclose(pfread);
		pfread = NULL;
		perror("fopen->pfwrite");
		return 2;
	}
	// copy and paste
	int ch = 0;
	while ((ch = fgetc(pfread)) != EOF)
	{
		fputc(ch, pfwrite);
	}
	// 判断 EOF or error
	if (ferror(pfread))
		printf("读文件遇到错误！\n");
	else if (feof(pfread))
		printf("遇到文件结尾，读文件结束！");
	//
	fclose(pfread);
	pfread = NULL;
	fclose(pfwrite);
	pfwrite = NULL;

	return 0;
}

7、文本文件和二进制文件

int main()
{
	FILE* pf = fopen("new1.txt", "wb");
	if (pf == NULL)
	{
		perror("fopen");
		return 1;
	}
	// 以二进制形式写入文件
	int a = 10000;
	fwrite(&a, sizeof(int), 1, pf);
	//
	fclose(pf);
	pf = NULL;
	return 0;
}

 

vs可用二进制编辑器打开二进制格式的文件。 

8、文件缓冲区

#define _CRT_SECURE_NO_WARNINGS -1
#include <stdio.h>
#include <Windows.h>  // sleep

// 文件缓冲区
int main()
{
	FILE* pf = fopen("test_file_buffer.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(在缓冲区)，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;
}