从文件读取时处理NSError？

Question

如果我这样做,我只是很好奇.

NSString *fileContents;    
NSError *fileError = nil;

fileContents = [[NSString stringWithContentsOfFile:fileOnDisk
                          encoding:NSMacOSRomanStringEncoding
                          error:&fileError] retain];

if(fileError != nil) {
    NSLog(@"Error : %@", [fileError localizedDescription]);
}

// Other Code ...
[fileContents release];

.

编辑(反映bbums评论)

.

NSString *fileOnDisk = @"/Users/Gary/Documents/Xcode/RnD/Maya.MEL";
NSError  *fileError; // Should this be *fileError = nil;
NSString *fileContents;
int       status = 0;

fileContents = [[NSString stringWithContentsOfFile:fileOnDisk
                          encoding:NSMacOSRomanStringEncoding
                          error:&fileError] retain];

if(fileContents == nil) {
    NSLog(@"FileError: %@", [fileError localizedDescription]);
    status = 1;
} else {
    NSLog(@"Success  : %@", fileContents);
}

// Clean up
[fileContents release];
[pool drain];
return status;

加里

Answer 1

NSError *fileError = nil;
....
if(fileError != nil)
....

那是不对的.你,直到你检查是否fileContents几乎等于零不能假定有关fileError返回按引用任何有价值的东西.永远不会.fileError在调用pass-error-by-reference方法之前设置为nil没有任何用处.

也就是说,你的代码应该读取(现在修复我不再从一个平面到另一个平面运行并在连接之间跳过WiFi ......):

NSString *fileContents;    
NSError *fileError;

fileContents = [[NSString stringWithContentsOfFile:fileOnDisk
                          encoding:NSMacOSRomanStringEncoding
                          error:&fileError] retain];

if(fileContents == nil) {
    NSLog(@"Error : %@", [fileError localizedDescription]);
    // ... i.e. handle the error here more
    return ...; // often returning after handling the errors, sometimes you might continue
}

// Other Code ...
[fileContents release];