fopen() 改为： if((fp=fopen("1s.txt","w+"))==NULL) 

fputc(p,fp); 改为：fprintf(fp,"%d",p); 
读语句前，加一句文件回绕到文件头： rewind(fp); 

#include <stdio.h>
main()
{ 
    FILE *fp; 
    char read[1000]; 
    char s; 
    long p; 
    if((fp=fopen("1s.txt","w+"))==NULL) 
    { 
        printf("\nOpen file error!press any key exit!"); 
        getchar(); 
        //exit(0); 
    } 
    p=123457; 
    s='\n'; 
    fprintf(fp,"%d",p); 
    fputc(s,fp); 
    fprintf(fp,"%d",p); 
    rewind(fp); 
    fgets(read,1000,fp); 
    printf("%s",read); 
    system("pause"); 
    return 0;
    }