c语言中strtok函数_在C语言中使用strtok（）和strtok_r（）函数

小咪咪 2023-02-28 06:11 70阅读 0赞

c语言中strtok函数

In this article, we’ll take a look at using the strtok() and strtok\_r() functions in C.

在本文中，我们将介绍如何在C语言中使用strtok（）和strtok\_r（）函数。

These functions are very useful, if you want to tokenize a string. C provides these handy utility functions to split our input string into tokens.

如果要标记字符串，这些功能非常有用。 C提供了这些方便的实用程序函数，可将我们的输入字符串拆分为标记。

Let’s take a look at using these functions, using suitable examples.

让我们使用合适的示例来看看如何使用这些功能。

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## 使用strtok（）函数 **(****Using the strtok() function****)** ##

First, let’s look at the strtok() function.

首先，让我们看一下strtok（）函数。

This function is a part of the `<string.h>` header file, so you must include it in your program.

此函数是`<string.h>`头文件的一部分，因此必须在程序中包含它。

#include <string.h>
    
    char* strtok(char* str, const char* delim);

This takes in an input string `str` and a delimiter character `delim`.

这将接受输入字符串`str`和定界符`delim` 。

`strtok()` will split the string into tokens based on the delimited character.

`strtok()`将根据定界字符将字符串拆分为标记。

We expect a list of strings from `strtok()`. But the function returns us a single string! Why is this?

我们期望从`strtok()`获得字符串列表。 但是该函数返回一个字符串！ 为什么是这样？

The reason is how the function handles the tokenization. After calling `strtok(input, delim)`, it returns the first token.

原因是该函数如何处理标记化。 调用`strtok(input, delim)` ，它返回第一个标记。

But we must keep calling the function again and again on a `NULL` input string, until we get `NULL`!

但是我们必须继续在`NULL`输入字符串上一次又一次地调用该函数，直到获得`NULL`为止！

Basically, we need to keep calling `strtok(NULL, delim)` until it returns `NULL`.

基本上，我们需要继续调用`strtok(NULL, delim)`直到返回`NULL` 。

Seems confusing? Let’s look at an example to clear it out!

似乎令人困惑？ 让我们看一个例子来清除它！

#include <stdio.h>
    #include <string.h>
    
    int main() {
        // Our input string
        char input_string[] = "Hello from JournalDev!";
    
        // Our output token list
        char token_list[20][20]; 
    
        // We call strtok(input, delim) to get our first token
        // Notice the double quotes on delim! It is still a char* single character string!
        char* token = strtok(input_string, " ");
    
        int num_tokens = 0; // Index to token list. We will append to the list
    
        while (token != NULL) {
            // Keep getting tokens until we receive NULL from strtok()
            strcpy(token_list[num_tokens], token); // Copy to token list
            num_tokens++;
            token = strtok(NULL, " "); // Get the next token. Notice that input=NULL now!
        }
    
        // Print the list of tokens
        printf("Token List:\n");
        for (int i=0; i < num_tokens; i++) {
            printf("%s\n", token_list[i]);
        }
    
        return 0;
    }

So, we have our input string “Hello from JournalDev!”, and we’re trying to tokenize it by spaces.

因此，我们有输入字符串“ Hello from JournalDev！”，我们正在尝试用空格标记它。

We get the first token using `strtok(input, " ")`. Notice the double quotes, as the delimiter is a single character string!

我们使用`strtok(input, " ")`获得第一个令牌。 注意双引号，因为定界符是单个字符串！

Afterwards, we keep getting tokens using `strtok(NULL, " ")` and loop until we get `NULL` from `strtok()`.

之后，我们继续使用`strtok(NULL, " ")`获取令牌并循环，直到从`strtok()`获取`NULL` 。

Let’s look at the output now.

现在让我们看一下输出。

**Output**

**输出量**

Token List:
    Hello
    from
    JournalDev!

Indeed, we seem to have got the correct tokens!

确实，我们似乎已经获得了正确的令牌！

Similarly, let’s now look at using `strtok_r()`.

同样，让我们现在来看一下使用`strtok_r()` 。

--------------------

## 使用strtok\_r（）函数 **(****Using the strtok\_r() function****)** ##

This function is very similar to the `strtok()` function. The key difference is that the `_r` means that this is a *re-entrant* function.

此函数与`strtok()`函数非常相似。 关键区别在于`_r`表示这是可*重入*函数。

**A reentrant function is a function that can be interrupted during its execution. This type of function can also be safely called again, to resume execution!**

**可重入函数是可以在其执行期间中断的函数。** **也可以再次安全地调用此类函数，以恢复执行！**

This is why it is a “re-entrant” function. Just because it can safely enter again!

这就是为什么它是“可重入”功能的原因。 只是因为它可以安全地再次进入！

Due to this fact, re-entrant functions are thread-safe, meaning that they can safely be interrupted by threads, just because they can resume again without any harm.

因此，重入函数是线程安全的，这意味着它们可以安全地被线程中断，因为它们可以再次恢复而不会造成任何伤害。

Now, similar to `strtok()`, the `strtok_r()` function is a thread-safe version of it.

现在，类似于`strtok()` ， `strtok_r()`函数是该线程的线程安全版本。

However, this has an extra parameter to it, called the *context*. We need this, so that the function can resume from the right place.

但是，这有一个额外的参数，称为*context* 。 我们需要这样做，以便函数可以从正确的位置恢复。

**NOTE**: If you’re using Windows, the equivalent function is *strtok\_s()*. *strtok\_r()* is for Linux / Mac based systems!

**注意** ：如果使用的是Windows，则等效功能为*strtok\_s（）* 。 *strtok\_r（）*适用于基于Linux / Mac的系统！

#include <string.h>
    
    char *strtok_r(char *str, const char *delim, char **context);

The `context` parameter is a pointer to the character, which `strtok_r` uses internally to save its state.

`context`参数是指向字符的指针， `strtok_r`内部使用该指针保存其状态。

Usually, we can just pass it from a user-declared pointer.

通常，我们可以从用户声明的指针传递它。

Let’s look at the same example for `strtok()`, now using `strtok_r()` (or `strtok_s()` on Windows).

让我们看一下`strtok()`的相同示例，现在使用`strtok_r()` （或Windows上的`strtok_s()` ）。

#include <stdio.h>
    #include <string.h>
    
    int main() {
        // Our input string
        char input_string[] = "Hello from JournalDev!";
    
        // Our output token list
        char token_list[20][20]; 
    
        // A pointer, which we will be used as the context variable
        // Initially, we will set it to NULL
        char* context = NULL;
    
        // To get the value of the context variable, we can pass it's address
        // strtok_r() to automatically populate this context variable, and refer
        // it's context in the future
        char* token = strtok_r(input_string, " ", &context);
    
        int num_tokens = 0; // Index to token list. We will append to the list
    
        while (token != NULL) {
            // Keep getting tokens until we receive NULL from strtok()
            strcpy(token_list[num_tokens], token); // Copy to token list
            num_tokens++;
            token = strtok_r(NULL, " ", &context); // We pass the context variable to strtok_r
        }
    
        // Print the list of tokens
        printf("Token List:\n");
        for (int i=0; i < num_tokens; i++) {
            printf("%s\n", token_list[i]);
        }
    
        return 0;
    }

**Output**

**输出量**

Token List:
    Hello
    from
    JournalDev!

While we get the same output, this version is better, since it is thread safe!

虽然我们得到相同的输出，但是此版本更好，因为它是线程安全的！

--------------------

## 结论 **(****Conclusion****)** ##

In this article, we learned about how we could use the strtok() and strtok\_r() functions in C, to tokenize strings easily.

在本文中，我们学习了如何在C中使用strtok（）和strtok\_r（）函数轻松地对字符串进行标记。

For similar content, do go through our tutorial section on [C programming][]!

对于类似的内容，请阅读我们有关[C编程的][C programming]教程部分！

## 参考资料 **(****References****)** ##

*  [Linux manual page][] on strtok() and strtok\_r() functions in C
    
    有关C语言中strtok（）和strtok\_r（）函数的[Linux手册页][Linux manual page]

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> 翻译自: [https://www.journaldev.com/42293/strtok-strtok-r-functions-c][https_www.journaldev.com_42293_strtok-strtok-r-functions-c]

c语言中strtok函数

[C programming]: https://www.journaldev.com/c-programming
[Linux manual page]: https://linux.die.net/man/3/strtok_r
[https_www.journaldev.com_42293_strtok-strtok-r-functions-c]: https://www.journaldev.com/42293/strtok-strtok-r-functions-c