详解C语言中fseek函数和ftell函数的使用方法
fseek函数: int fseek(FILE * _File,long _Offset,int _Origin); 函数设置文件指针stream的位置。如果执行成功,stream将指向以fromwhere为基准,偏移offset(指针偏移量)个字节的位置,函数返回0。如果执行失败则不改变stream指向的位置,函数返回一个非0值。 #include<stdio.h> #define N 5 typedef struct student{ long sno; char name[10]; float score[3]; }STU; void fun(char*filename,STU n) { FILE*fp; fp=fopen(filename,"rb+"); fseek(fp,-1L*sizeof(STU),SEEK_END); fwrite(&n,sizeof(STU),1,fp); fclose(fp); } int main()/*修改覆盖最后一个学生数据*/ { STU t[N]={ {10001,"MaChao",91,92,77},{10002,"CaoKai",75,60,88},{10003,"LiSi",85,70,78},{10004,"FangFang",90,82,87},{10005,"ZhangSan",95,80,88} }; STU n={10006,"ZhaoSi",55,68},ss[N]; int i,j;FILE*fp; fp=fopen("student.dat","wb"); fwrite(t,N,fp); fclose(fp); fp=fopen("student.dat","rb"); fread(ss,fp); fclose(fp); printf("nThe original data:nn"); for(j=0;j<N;j++) { printf("nNo:%ldName:%-8sScores:",ss[j].sno,ss[j].name); for(i=0;i<3;i++) printf("%6.2f",ss[j].score[i]); printf("n"); } fun("student.dat",n); printf("nThe data after modifing:nn"); fp=fopen("student.dat","rb"); fread(ss,fp); fclose(fp); for(j=0;j<N;j++) { printf("nNo:%ldName:%-8sScores:",ss[j].score[i]); printf("n"); } return 0; } ftell函数 long len = ftell(fp) eg1: #include <stdio.h> int main( void ) { FILE *stream; stream = fopen( "MYFILE.TXT","w+" ); fprintf( stream,"This is a test" ); printf( "The file pointer is at byte %ldn",ftell( stream ) ); fclose( stream ); return(0); } eg2: #include <stdio.h> #include <stdlib.h> int main() { FILE *fp; int flen; char *p; /* 以只读方式打开文件 */ if ( (fp = fopen( "1.txt","r" ) ) == NULL ) { printf( "nfile open errorn" ); exit( 0 ); } fseek( fp,0L,SEEK_END ); /* 定位到文件末尾 */ flen = ftell( fp ); /* 得到文件大小 */ p = (char *) malloc( flen + 1 ); /* 根据文件大小动态分配内存空间 */ if ( p == NULL ) { fclose( fp ); return(0); } fseek( fp,SEEK_SET ); /* 定位到文件开头 */ fread( p,flen,fp ); /* 一次性读取全部文件内容 */ p[flen] = ' '; /* 字符串结束标志 */ printf( "%s",p ); fclose( fp ); free( p ); return(0); }
#include <stdio.h> main() { FILE *myf; long f1; /* 此处将f1设置为long 可以读取更长的文件 */ myf = fopen( "1.txt","rb" ); fseek( myf,SEEK_END ); f1 = ftell( myf ); fclose( myf ); printf( “ % d n ”,f1 ); } (编辑:李大同) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |