#include<iostream>#include <fstream>#include <string>#include <string.h>using namespace std;void main(){//在文件中寫入學號和科目string number;string name;ofstream outstuf ; outstuf.open( "test.txt" , ios::app|ios::binary ) ; if ( !outstuf ) { cerr << "文件不存在" << endl ; abort(); }cin>>number;number=number+" ";outstuf.seekp(0,ios::end); //多這名，文件指針移到尾outstuf<<number.c_str();怎么用fseek（）使得指針能指向到number后面，指向文件里面number的后面？
3 回答
qq_笑_17
TA貢獻1818條經驗 獲得超7個贊
int fseek(FILE *stream, long offset, int fromwhere);函數設置文件指針stream的位置。如果執行成功，stream將指向以fromwhere（偏移起始位置：文件頭0(SEEK_SET)，當前位置1(SEEK_CUR)，文件尾2(SEEK_END)）為基準，偏移offset（指針偏移量）個字節的位置。如果執行失敗(比如offset超過文件自身大小)，則不改變stream指向的位置。
也就是寫成 fseek(outstuf,0,2);
繁星點點滴滴
TA貢獻1803條經驗 獲得超3個贊
函數fseek使用指南
1.函數原型：
int fseek ( FILE * stream, long int offset, int origin );
2. 函數功能：
Sets the position indicator associated with the stream to a new position.
For streams open in binary mode, the new position is defined by adding offset to a reference position specified by origin.
For streams open in text mode, offset shall either be zero or a value returned by a previous call to ftell, and origin shall necessarily be SEEK_SET.
If the function is called with other values for these arguments, support
depends on the particular system and library implementation
(non-portable).
The end-of-file internal indicator of the stream is cleared after a successful call to this function, and all effects from previous calls to ungetc on this stream are dropped.
On streams open for update (read+write), a call to fseek allows to switch between reading and writing.
3. 函數參數
stream
Pointer to a FILE object that identifies the stream.
offset
Binary files: Number of bytes to offset from origin.
Text files: Either zero, or a value returned by ftell.
origin
Position used as reference for the offset. It is specified by one of the following constants defined in <cstdio> exclusively to be used as arguments for this function:
Constant
Reference position
SEEK_SET Beginning of file
SEEK_CUR Current position of the file pointer
SEEK_END End of file *
* Library implementations are allowed to not meaningfully support SEEK_END (therefore, code using it has no real standard portability).
4. 返回值
If successful, the function returns zero.
Otherwise, it returns non-zero value.
If a read or write error occurs, the error indicator (ferror) is set.
5. 例程
#include <stdio.h>
int main ()
{
FILE * pFile;
pFile = fopen ( "example.txt" , "wb" );
fputs ( "This is an apple." , pFile );
fseek ( pFile , 9 , SEEK_SET );
fputs ( " sam" , pFile );
fclose ( pFile );
return 0;
}
After this code is successfully executed, the file example.txt contains:
This is a sample
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