创建，结果在一个字符串的文件*流 [英] Creating a FILE * stream that results in a string

问题描述

我在寻找一种方式在 FILE * 来的一些功能，使功能可以写入与 fprintf中。这是很容易，如果我想输出在磁盘上的实际的文件转起来，说。但我想反而是让所有的输出作为一个字符串（的char * ）。我想那种API是：

I'm looking for a way to pass in a FILE * to some function so that the function can write to it with fprintf. This is easy if I want the output to turn up in an actual file on disk, say. But what I'd like instead is to get all the output as a string (char *). The kind of API I'd like is:

/** Create a FILE object that will direct writes into an in-memory buffer. */
FILE *open_string_buffer(void);

/** Get the combined string contents of a FILE created with open_string_buffer
    (result will be allocated using malloc). */
char *get_string_buffer(FILE *buf);

/* Sample usage. */
FILE *buf;
buf = open_string_buffer();
do_some_stuff(buf);   /* do_some_stuff will use fprintf to write to buf */
char *str = get_string_buffer(buf);
fclose(buf);
free(str);

在的glibc 头似乎表明，一个文件可以设置钩函数来执行实际的读写。在我来说，我想我要的写勾串的拷贝追加到一个链表，并为那里是一个 get_string_buffer 函数，计算出总长度列表中分配内存它，并在正确的位置，然后再复制的每一项内容。

The glibc headers seem to indicate that a FILE can be set up with hook functions to perform the actual reading and writing. In my case I think I want the write hook to append a copy of the string to a linked list, and for there to be a get_string_buffer function that figures out the total length of the list, allocates memory for it, and then copies each item into it in the correct place.

我的目标的东西，可以被传递给一个函数，如 do_some_stuff ，而不该功能需要知道任何其他比它有一个 FILE * 可写。

I'm aiming for something that can be passed to a function such as do_some_stuff without that function needing to know anything other than that it's got a FILE * it can write to.

有没有大概是这样一个现有的实现？这似乎是做一个有用的C-友好的事情 - 假设我是对有关文件扩展

Is there an existing implementation of something like this? It seems like a useful and C-friendly thing to do -- assuming I'm right about the FILE extensibility.

推荐答案

如果便携性是不是对你很重要，你可以采取的 fmemopen 和 open_memstream 。他们是GNU扩展，因此仅适用于glibc的系统。虽然看起来好像他们是POSIX.1-2008的一部分（ fmemopen 和 open_memstream ）。

If portability is not important for you, you can take a look on fmemopen and open_memstream. They are GNU extensions, hence only available on glibc systems. Although it looks like they are part of POSIX.1-2008 (fmemopen and open_memstream).

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