C语言读写文件

void appendwt(){
	FILE *pFile = fopen("data.txt","ab+");//使用"ab+"每次都插入到最后面,调用fseek也没用
	char *str="hello,world!45%13ad2014/23/13add\n";
	    fwrite(str,1,strlen(str),pFile);
	    fflush(pFile);
	    fclose(pFile);
}

void randwt(){
FILE *fp;
        fp=fopen("overwrite.bin","rb+"); //使用rb+模式,可以往半中间插入数据,定义到任何位置
        {
            if(-1 == (fseek(fp,9, SEEK_SET))) /从第9字节开始abcde
                    printf("seek error\n");
            fwrite("abcde",1, 5, fp);
            fflush(fp);//flush来刷新流，每次读写后都希望立即看到结果，不用重新打开关闭
            fclose(fp);
        }
        else
        {
            printf("fopen error");
        }
}

void overwt() {
	FILE *pFile = fopen("data.txt","w+");
	    fwrite("hello,world!",1,strlen("hello,world!"),pFile);
	    fflush(pFile);                    
            //fseek来移动文件的指针，它指向文件下一个要写入的位置
	    fseek(pFile,0,SEEK_SET);        //文件指针设为起点，写操作覆盖原来的内容
	    fwrite("欢迎访问",1,strlen("欢迎访问"),pFile);
	    fseek(pFile,0,SEEK_END);        //文件指针设为终点
	    int len = ftell(pFile);         //获取文件字节数
	    char* ch = (char*)malloc(sizeof(char)* (len+1));    //分配内存，多一个字节
	    memset(ch,0,(len+1));           //清0
	//  fseek(pFile,0,SEEK_SET);        //文件指针指向头部
	    rewind(pFile);
	    fread(ch,1,len,pFile);          //读取文件
	    fclose(pFile);
	    printf("%s",ch);
}

typedef struct {
	char c;
	int h;
	short n;
	long m;
	float f;
	double d1;
	char *s;
	double d2;
} st;

void struwt() {

	FILE *fp;
	st sa, sb; //定义结构体
	char *str = "abcdefg"; //结构体赋值
	sa.c = ‘K‘;
	sa.h = -3;
	sa.n = 20;
	sa.m = 100000000;
	sa.f = 33.32f;
	sa.d1 = 78.572;
	sa.d2 = 33.637;
	sa.s = str;
	fp = fopen("st.txt", "w+"); //打开要写的文件
	if (!fp) {
		printf("errror!\n");
		exit(-1);
	}
	printf("sa:c=%c,h=%d,n=%d,m=%d,f=%f,d1=%f,s=%s,d2=%f\n", sa.c, sa.h, sa.n,
			sa.m, sa.f, sa.d1, sa.s, sa.d2);
	printf("sizeof(sa)=%d:&c=%x,&h=%x,&n=%x,&m=%x,&f=%x,&d1=%x,&s=%x,&d2=%x\n",
			sizeof(sa), &sa.c, &sa.h, &sa.n, &sa.m, &sa.f, &sa.d1, &sa.s,
			&sa.d2);

	fwrite(&sa, sizeof(sa), 1, fp); //写入结构体
	rewind(fp); //重新指向流
	fread(&sb, sizeof(sb), 1, fp); //用sb读取
	printf("sb:c=%c,h=%d,n=%d,m=%d,f=%f,d1=%f,s=%s,d2=%f\n", sb.c, sb.h, sb.n,
			sb.m, sb.f, sb.d1, sb.s, sb.d2);
	fclose(fp); //关闭指针
}

//从文件读取结构体
void strurd() {
	FILE *fp;
	st sb;
	fp = fopen("st.txt", "r"); //打开文件
	if (!fp) {
		printf("errror!\n");
		exit(-1);
	}
	fread(&sb, sizeof(sb), 1, fp); //读取结构体
	printf("sb:c=%c,h=%d,n=%d,m=%d,f=%f,d1=%f,s=%s,d2=%f\n", sb.c, sb.h, sb.n,
			sb.m, sb.f, sb.d1, sb.s, sb.d2);
	printf("sizeof(sb)=%d:&c=%x,&h=%x,&n=%x,&m=%x,&f=%x,&d1=%x,&s=%x,&d2=%x\n",
			sizeof(sb), &sb.c, &sb.h, &sb.n, &sb.m, &sb.f, &sb.d1, &sb.s,
			&sb.d2);

	fclose(fp);
}