從寫入stdio數據沒有將其寫入文件

Question

我遇到了使用stdio命令操縱文件中的數據的問題。簡而言之，當我將數據寫入一個文件時，write會返回一個int值，表示它是成功的，但是當我讀取它時，我只能得到舊數據。

下面的代碼的精簡版：

fd = open(filename,O_RDWR|O_APPEND); 

struct dE *cDE = malloc(sizeof(struct dE)); 

//Read present data 
printf("\nreading values at %d\n",off); 
printf("SeekStatus <%d>\n",lseek(fd,off,SEEK_SET)); 
printf("ReadStatus <%d>\n",read(fd,cDE,deSize)); 

printf("current Key/Data <%d/%s>\n",cDE->key,cDE->data); 

printf("\nwriting new values\n"); 
//Change the values locally 
cDE->key = //something new 
cDE->data = //something new 

//Write them back 
printf("SeekStatus <%d>\n",lseek(fd,off,SEEK_SET)); 
printf("WriteStatus <%d>\n",write(fd,cDE,deSize)); 

//Re-read to make sure that it got written back 
printf("\nre-reading values at %d\n",off); 
printf("SeekStatus <%d>\n",lseek(fd,off,SEEK_SET)); 
printf("ReadStatus <%d>\n",read(fd,cDE,deSize)); 

printf("current Key/Data <%d/%s>\n",cDE->key,cDE->data); 

此外，這裏的德結構的情況下，你想知道：

struct dE { 
    int key; 
    char data[DataSize]; 
}; 

此打印：

reading values at 1072 
SeekStatus <1072> 
ReadStatus <32> 
current Key/Data <27/old> 

writing new values 
SeekStatus <1072> 
WriteStatus <32> 

re-reading values at 1072 
SeekStatus <1072> 
ReadStatus <32> 
current Key/Data <27/old> 

Answer 1

從open呼叫中刪除|O_APPEND。