C语言 fprintf()含税总是写入失败

写了一个关于fprintf的程序，总是失败，不知是什么原因：

#include<stdio.h>

int main(void)

{
    FILE *fp;
    
    int i,j,k;
    
    char ch;
    
    fp=fopen("666.txt","a+");    
    
    if(fp==NULL)
    
    printf("Open is failed!");
    
    fscanf(fp," %d  %d  %c",&i,&j,&ch);
    
    printf("**the ijch is : %d %d %c",i,j,ch);
    
    k=fprintf(fp,"**the ijch is : %d %d %c",i,j,ch);
    
    printf("the K is %d.\n",k);
    
    fclose(fp);    
    
    return 0;    
    
    
}

这里的 i j ch 分别是 556 778 s ，程序运行的结果如下：

即使将程序调整简单点，

#include<stdio.h>

int main(void)

{
    FILE *fp;
    
    int i,j,k,m=226;
    
    char ch;
    
    fp=fopen("666.txt","a+");    
    
    if(fp==NULL)
    
    printf("Open is failed!");
    
    fscanf(fp," %d  %d  %c",&i,&j,&ch);
    
    printf("**the ijch is : %d %d %c",i,j,ch);    
    
    k=fprintf(fp,"%d",m);    
    
    printf("the K is %d.\n",k);
    
    fclose(fp);    
    
    return 0;    
    
    
}

K都是-1，写入都是失败的。 我没看出是哪里出错了，请指点。

#include<stdio.h>
int main(){
FILE *fp;

    int i,j,k;

    char ch;

    fp=fopen("666.txt","r");    

    if(fp==NULL)

        printf("Open is failed!");

    fscanf(fp," %d  %d  %c",&i,&j,&ch);

    printf("**the ijch is : %d %d %c ",i,j,ch);

    fclose(fp);

    fp=fopen("666.txt","a+");    

    if(fp==NULL)

        printf("Open is failed!");

    k=fprintf(fp,"%d %d %c",i,j,ch);

    printf("the K is %d.\n",k);

    fclose(fp);
    return 0;  
}

运行结果：

#include <stdio.h>

int main(void)
{
    FILE *fp;
    int i, j, k;
    char ch;
    {
        fp = fopen("666.txt", "r");
        fscanf(fp, " %d  %d  %c", &i, &j, &ch);
        fclose(fp);
        printf("**the ijch is : %d %d %c", i, j, ch);
    }

    {
        fp = fopen("666.txt", "a+");
        k = fprintf(fp, "**the ijch is : %d %d %c\n", i, j, ch);
        printf("the K is %d.\n", k);
        fclose(fp);
    }

    return 0;
}