有条件设置一个变量，如果它是NULL [英] Conditionally set a variable if it's NULL

问题描述

在通过步进一个 sqlite3_stmt ，我想核对 NULL ，而不是商店的返回值它和检查对存储的值。

When stepping through a sqlite3_stmt, I'd like to check against a return value of NULL rather than store it and check against the stored value.

下面是我现在在做什么：

Here's what I'm doing now:

char *email = (char *)sqlite3_column_text(statement, 10);
if (email == NULL) email = "";

和这里是我想的如的是做，减去双呼叫列：

And here is what I'd like to be doing, minus the double-call to column:

char *email = ((char *)sqlite3_column_text(statement, 10)) ? (char *)sqlite3_column_text(statement, 10) : "";

有没有一些方法来恩preSS第二前pression更简洁？我必须做很多重复这些，所以我在寻找短暂。

Is there some way to express the second expression more concisely? I have to do a lot of these repetitively, so I'm looking for brevity.

我知道这是控制流的问题，而不是用SQLite的API本身的问题，但你有它。我想不出一个好办法做到这一点。

I know this is a problem of control flow rather than a problem with the SQLite API itself but there you have it. I can't think of a good way to do this.

推荐答案

一个的 GNU扩展到C 使三元条件运算符来评估自身情况，如果这是真的，并没有什么第一分公司：

A GNU extension to C allows the ternary conditional operator to evaluate to its condition if it's true and there's nothing in the first branch:

char *email = (char *)sqlite3_column_text(statement, 10);
email = email ? : "";

或者，更确切地说你要找你说什么

or, more exactly what you say you're looking for

char * email = (char *)sqlite3_column_text(statement, 10) ? : "";

这铿锵编译时也有效。

另一种可能性是：

char *email = (char *)sqlite3_column_text(statement, 10);
email = (NULL == email) ? email : "";

不过，我想我会建议只是你的第一个选项去。做一个code片段，如果你做了很多。

But I think I'd recommend just going with your first option. Make a code snippet if you're doing it a lot.

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