麻煩在結構中傳遞C字符串

Question

我無法從傳遞的結構中獲取char *字符串。我有以下代碼：

typedef struct { 
    NSInteger id; 
    char *title; 
} Movie; 

... 

Movie movie = [self randomMovie]; 

NSInteger movieID = movie.id; 
NSString *movieTitle = [NSString stringWithUTF8String:movie.title]; 
NSLog(@"movieTitle: %@", movieTitle); 

... 

- (Movie)randomMovie { 
sqlite3_stmt *statement; 
NSString *query = @"SELECT id, title FROM movies ORDER BY RANDOM() LIMIT 1;"; 

Movie movie; 

if (sqlite3_prepare_v2(database, [query UTF8String], -1, &statement, nil) == SQLITE_OK) { 
    if (sqlite3_step(statement) == SQLITE_ROW) { 
     // Get the id and title of the first 
     movie.id = sqlite3_column_int(statement, 0); 
     movie.title = (char *)sqlite3_column_text(statement, 1); 
    } 
} 

NSLog(@"Random movie %d title: %@", movie.id, [NSString stringWithUTF8String:movie.title]); 

sqlite3_finalize(statement); 
return movie; 
} 

這使我的輸出：

2013-03-13 10:10:39.438 Fabflix[89156:c07] Random movie 872011 title: Ray 
2013-03-13 10:10:39.439 Fabflix[89156:c07] movieTitle: (null) 

有誰知道爲什麼標題字符串沒有被正確地從randomMovie通過呢？謝謝！

Answer 1

我對sqlite3 C API並不熟悉，但是您確定sqlite3_finalize()調用不會銷燬從sqlite3_column_text()返回的C字符串嗎？你可能需要strdup()那個東西（然後記得free()它）。

更新：是的，從文檔：

返回的指針是有效的，直到如上所述發生類型轉換，或直到sqlite3_step（）或sqlite3_reset（）或sqlite3_finalize（）被調用。用於保存字符串和BLOB的內存空間會自動釋放。

Answer 2

由sqlite3_column_text is released as soon as you call sqlite3_finalize返回的內存。您需要先將值複製到您自己的字符串中。

typedef struct { 
    NSInteger id; 
    NSString *title; 
} Movie; 

/* ... */ 

movie.title = 
    [NSString stringWithUTF8String:(char *)sqlite3_column_text(statement, 1)];