Binary input (fread), output (fwrite) of files

    1.fwrite (binary output)

    // size_t fwrite(const void* ptr, size_t size, size_t count, FILE* stream);
    // const void* ptr: pointer to the data to be written
    // size_t size: one element size of the data to be written
    // size_t count: the number of elements of the data to be written
    // FILE* stream: the file pointer pointing to the file to be written
    // size_t fwrite (return value): the actual number of elements output, not necessarily equal to count

#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
struct S
{
	char name[20];
	int age;
	float score;
};
int main()
{
	struct S s1 = { "zhangsan",24,93.5f };
	//打开文件
	FILE* pf = fopen("test.dat", "wb");
	if (pf == NULL)
	{
		perror("fopen");
		return 1;
	}
	//写文件
	fwrite(&s1, sizeof(struct S), 1, pf);	
		//		fwrite是以二进制形式输出（写文件），所以文件打开之后会出现部分内容（准确来说是除了字符串以外的其他类型的内容，因为字符串以二进制形式存储和以文本形式存
		// 储是一样的）不认识或者乱码，因为二进制形式存储和文本形式存储是截然不同的。为解决不认识二进制形式的输出内容这一问题，我们可以再以二进制形式读取（输入）这些内容
	
	//关闭文件
	fclose(pf);
	pf = NULL;
	return 0;
}

2.fread (binary input)

    // size_t fread(void* ptr, size_t size, size_t count, FILE* stream);
    // void* ptr: Pointer to the memory block used to store the read data. This memory block can store at least count elements.
    // size_t size: the size of an element of the data to be read
    // size_t count: the number of elements of the data to be read
    // FILE* stream: file pointer pointing to the file to be read
    // size_t fread (return value): fread actual The number of elements read, if the count parameter is 5, and the number of elements actually read by fread is 3, then the return value is 3 

#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
struct S
{
	char name[20];
	int age;
	float score;
};
int main()
{
	struct S s2 = {0};
	//打开文件
	FILE* pf = fopen("test.dat", "rb");
	if (pf == NULL)
	{
		perror("fopen");
		return 1;
	}
	//写文件
	fread(&s2, sizeof(struct S), 1, pf);
		//		fread是以二进制形式输入（读文件），"test.dat"是文本文件，里边存放了二进制信息，二进制信息在文本文件中我们是看不懂的（除了字符内容，字符的
		// 二进制形式和文本形式是一样的），fread可以读取到文本文件中的二进制信息
	printf("%s %d %f\n", s2.name, s2.age, s2.score);	//zhangsan 24 93.500000
//关闭文件
	fclose(pf);
	pf = NULL;
	return 0;
}