解析$ PATH变量并将目录名保存到一个字符串数组中 [英] Parse $PATH variable and save the directory names into an array of strings

问题描述

我想解析Linux的$ PATH变量，然后将以'：'分隔的目录名保存到一个字符串数组中。

I知道这是一个简单的任务，但我卡住了，任何帮助都会很好。

到目前为止，我的代码是这样的，但有些不对。

  char ** array; 
 char * path_string; 
 char * path_var = getenv（PATH）; 
 int size_of_path_var = strlen（path_var）; 
 
 path_string = strtok（path_var，：）; 
 while（path_string！= NULL）{
 ss = strlen（path_string）
 array [i] =（char *）malloc（ss + 1）; 
 array [i] = path_string; //这实际上是我想要为每条路径做的所有事情
 i ++; 
 path_string = strtok（NULL，：）; 
 
  

解决方案

<2>代码，几乎总结了评论：

• 您创建一个公共缓冲区（由 getenv
• 你不知道缓冲区中有多少变量，所以你根本不会分配数组数组！$ /

/ ul>



让我使用strtok提出一个工作实现 not ，从而允许检测空路径（并将其替换为）。 ，Jonathan暗示）。使用 gcc -Wall -Wwrite-strings ：

编译没有任何警告：



  #include< stdio.h> 
 #include< string.h> 
 #include< stdlib.h> 
 
 int main（）
 {
 const char ** array; 
 const char * orig_path_var = getenv（PATH）; 
 char * path_var = strdup（orig_path_var？orig_path_var：）; //如果PATH为NULL，则不太可能
 const char * the_dot =。; 
 int j; 
 int len = strlen（path_var）; 
 int nb_colons = 0; 
 char pathsep ='：'; 
 int current_colon = 0; 
 
 //首先计算我们有多少条路径，而拆分就像strtok那样，对于（j = 0; j< len; j ++）
 {
 if（path_var [j] == pathsep）
 {
 nb_colons ++; 
 path_var [j] ='\0'; 
 
 
 
 //分配字符串数组
 array = malloc（（nb_colons + 1）* sizeof（* array））; 
 
 array [0] = path_var; //第一条路径
 
 //其余路径
 for（j = 0; j< len; j ++）
 {
 if（path_var [j] == '\0'）
 {
 current_colon ++; 
 array [current_colon] = path_var + j + 1; 
 if（array [current_colon] [0] =='\0'）
 {
 //特殊情况：如果路径为空，则添加点
 array [current_colon] = the_dot; （j = 0; j  {
 
 
 
 
 
 $ b printf（Path％d：<％s> \\\
，j，array [j]）; 
} 
 
 return（0）; 
 
 $ / code> 

操作细节：





• 制作env字符串的副本以避免屠杀它$
• 计数冒号（为了使它与windows一起工作，只需替换为<$ c
  
• 
  
• 根据冒号数量+ 1分配数组（1个符号比分隔符数量更多！）$ / $> b $ b
• 第二遍以再次遍历字符串，并将其填充到标记化字符串的某些部分（不需要再次分配，原始字符串已分配）。
  
• 特殊情况：空路径：替换为。。可能会显示警告，告诉用户这是不安全的。


• 打印结果





I want to parse the $PATH variable of Linux, and then save the directory names that are getting separated with ':' into an array of strings.

I know it's a simple task but I am stuck and any help would be nice.

My code so far is something like this but something ain't right.

char **array;
char *path_string;
char *path_var = getenv("PATH");
int size_of_path_var = strlen(path_var);

path_string = strtok(path_var, ":");
while (path_string != NULL) {
    ss = strlen(path_string)
    array[i] = (char *)malloc(ss + 1);
    array[i] = path_string; //this is actually all i want to do for every path
    i++;
    path_string = strtok(NULL, ":");
}

解决方案

2 main things wrong with your code, pretty much summarized by the comments:

• you strtok a public buffer (returned by getenv)
• you don't know how many variables will be in the buffer so you don't allocate the array of arrays at all!

Let me propose a working implementation not using strtok, and thus allowing to detect empty path (and replace it by . as Jonathan hinted). Compiles without any warnings using gcc -Wall -Wwrite-strings:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int main()
{
    const char **array;
    const char *orig_path_var = getenv("PATH");
    char *path_var = strdup(orig_path_var ? orig_path_var : ""); // just in case PATH is NULL, very unlikely
    const char *the_dot = ".";
    int j;
    int len=strlen(path_var);
    int nb_colons=0;
    char pathsep = ':';
    int current_colon = 0;

    // first count how many paths we have, and "split" almost like strtok would do
    for (j=0;j<len;j++)
    {
        if (path_var[j]==pathsep)
        {
            nb_colons++;
            path_var[j] = '\0';
        }       
    }

    // allocate the array of strings
    array=malloc((nb_colons+1) * sizeof(*array));

    array[0] = path_var;  // first path

    // rest of paths
    for (j=0;j<len;j++)
    {
        if (path_var[j]=='\0')
        {
            current_colon++;
            array[current_colon] = path_var+j+1;
            if (array[current_colon][0]=='\0')
            {
                // special case: add dot if path is empty
                array[current_colon] = the_dot;
            }

        }
    }

    for (j=0;j<nb_colons+1;j++)
    {
        printf("Path %d: <%s>\n",j,array[j]);
    }

    return(0);
}

Details of the operations:

• make a copy of the env string to avoid butchering it
• count the colons (to make it work with windows, just replace with ;) and tokenize
• allocate the array according to number of colons + 1 (1 more token than number of separators!)
• second pass to go through the string again and fill it with parts of the tokenized string (no need to allocate again, the original string is already allocated)
• special case: empty path: replace by .. Could display a warning to tell the user that this is not safe.
• print the result

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