小编use*_*174的帖子

我有这个代码在iphone中的目录中创建一个文本文件:

NSArray *paths = NSSearchPathForDirectoriesInDomains
    (NSDocumentDirectory, NSUserDomainMask, YES);

    NSString *documentsDirectory = [paths objectAtIndex:0];

    NSString *fileName = [NSString stringWithFormat:@"%@/file.txt",
                          documentsDirectory];

    NSString *content = @"my first text";

    NSError *error;

    if ([[NSFileManager defaultManager] fileExistsAtPath:fileName] == NO) {

    [content writeToFile:fileName
              atomically:YES
                encoding:NSStringEncodingConversionAllowLossy
                   error:&error];

    }else{

        [content writeToFile:fileName
                  atomically:YES
                    encoding:NSStringEncodingConversionAllowLossy
                       error:&error];

    }

代码工作正常,直到在某个时间它不再工作,并返回以下错误:

错误域= NSCocoaErrorDomain代码= 517"操作无法完成.(Cocoa错误517.)"UserInfo = 0x8c852b0 {NSFilePath =/Users/williamlima/Library/Application Support/iPhone Simulator/7.1/Applications/B5781B9E-3915- 4656-83D4-5E0FB6486567/Documents/file.txt,NSStringEncoding = 1}

我怎么能解决这个问题？

我在sql中有这样的语法：

UPDATE fazerbem_carrinho_historico 
SET pendencia_pago = '10.00', 
    pendenciahistorico = pendenciahistorico + '12' 
WHERE data_compra = '76'

假设列内pendenciahistorio已经有了'16'值，会发生什么，所以我给出更新，存储值1612，但它们保存了总和16 + 12，因为pendenciahistorico列是 varchar，如何解决它？