计算大小为基带64 codeD消息 [英] Calculate the size to a Base 64 encoded message

问题描述

我有我的基地64编码我现在一个二进制字符串，我需要知道手前的最后基地64 EN codeD字符串大小会。

I have a binary string that I am encoding in Base 64. Now, I need to know before hand the size of the final Base 64 encoded string will be.

有什么方法来计算？

是这样的：

BinaryStringSize为64KB
恩codedBinaryStringSize将编码后127KB。

BinaryStringSize is 64Kb EncodedBinaryStringSize will be 127Kb after encoding.

呵呵，code是在C

Oh, the code is in C.

感谢。

推荐答案

如果你做的Base64 的究竟的右，这包括用填充 = 字符结束，你打破它一个 CR LF 每72个字符，答案可以找到：

If you do Base64 exactly right, and that includes padding the end with = characters, and you break it up with a CR LF every 72 characters, the answer can be found with:

code_size    = ((input_size * 4) / 3);
padding_size = (input_size % 3) ? (3 - (input_size % 3)) : 0;
crlfs_size   = 2 + (2 * (code_size + padding_size) / 72);
total_size   = code_size + padding_size + crlfs_size;

在C语言中，你也可以用 \\ 0 - 字节终止，所以会在那里一个额外的字节，你可以在需要的长度检查每code端为你写他们，所以如果你只是找你传递什么的malloc（），你实际上可能preFER版本即浪费的几个字节，以使编码更简单：

In C, you may also terminate with a \0-byte, so there'll be an extra byte there, and you may want to length-check at the end of every code as you write them, so if you're just looking for what you pass to malloc(), you might actually prefer a version that wastes a few bytes, in order to make the coding simpler:

output_size = ((input_size * 4) / 3) + (input_size / 96) + 6;

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