为什么我的数组的先前元素发生变化（C中的字符串数组）

Question

我正在构建一个外壳历史记录功能，以接收一个字符串，并在程序运行时将其添加到字符串数组中。

我的问题是，每当我用新行（字符串）更新数组时，缓存中的前一个元素就会被CWD（当前工作目录）填充，但是我需要保留设置它的前一个字符串。

这是我的主循环，获取字符串并尝试使用缓存功能存储历史记录：

//prints out the cwd; then loops to take in the line, split it up into arguments, and attempt to execute it
//while lsh_execute returns 0, then frees up the allocated space
void lsh_loop(void)
{
  char *line;               //pointer to a char (the beg. of an array of chars)
  char *cache[10] = {NULL};     //history array
  char **args;              //pointer to a pointer of a char...
  int status, counter = 0, i, j;

  do {
    printf("%s>", getcwd(0,0));     //print cwd
    line = lsh_read_line();     //call read line
    counter = lsh_cache_line(counter,line, cache);
    printf("This is counter:%i\n", counter);        

    for(i=0; i<10; i++){
      printf("This is cache[%i]:%s\n", i, cache[i]);
    }

    args = lsh_split_line(line);    //split line
    status = lsh_execute(args);     //execute the split args

    free(line);             //free memory
    free(args);
  } while (status);         //continue as long as execute returns 1

}

在此函数中，我将输入字符串行复制到字符串数组：

int lsh_cache_line(int counter,char *line, char *cache[10]){

  (cache[counter]) = line;
  printf("This is cache[%i]:%s\n", counter, cache[counter]);
  counter++;
  counter = counter % 10;
  return counter; 

}

这是我程序的输出：

paul@paul-VirtualBox:~/Desktop$ gcc shell.c
paul@paul-VirtualBox:~/Desktop$ ./a.out
/home/paul/Desktop>HI
This is cache[0]:HI
This is counter:1
This is cache[0]:HI
This is cache[1]:(null)
This is cache[2]:(null)
This is cache[3]:(null)
This is cache[4]:(null)
This is cache[5]:(null)
This is cache[6]:(null)
This is cache[7]:(null)
This is cache[8]:(null)
This is cache[9]:(null)
lsh: No such file or directory
/home/paul/Desktop>this is my problem
This is cache[1]:this is my problem
This is counter:2
This is cache[0]:/home/paul/Desktop
This is cache[1]:this is my problem
This is cache[2]:(null)
This is cache[3]:(null)
This is cache[4]:(null)
This is cache[5]:(null)
This is cache[6]:(null)
This is cache[7]:(null)
This is cache[8]:(null)
This is cache[9]:(null)
lsh: No such file or directory
/home/paul/Desktop>it overwrites my previous string with the cwd
This is cache[2]:it overwrites my previous string with the cwd
This is counter:3
This is cache[0]:/home/paul/Desktop
This is cache[1]:/home/paul/Desktop
This is cache[2]:it overwrites my previous string with the cwd
This is cache[3]:(null)
This is cache[4]:(null)
This is cache[5]:(null)
This is cache[6]:(null)
This is cache[7]:(null)
This is cache[8]:(null)
This is cache[9]:(null)
lsh: No such file or directory
/home/paul/Desktop>^C
paul@paul-VirtualBox:~/Desktop$ 

我尝试了各种声明和初始化字符串数组的方法，但是这种方法似乎效果最好。

我究竟做错了什么？

Answer 1

cache没有存储字符串的空间。

诸如strdup东西会创建存储，但是您稍后需要free内存。

int lsh_cache_line(int counter,char *line, char *cache[10]){

 (cache[counter]) = strdup(line);
 printf("This is cache[%i]:%s\n", counter, cache[counter]);
 counter++;
 counter = counter % 10;
 return counter; 

}

字符串有10个插槽，但是字符串值没有存储空间。 您需要分配一些内存。

Answer 2

我敢打赌，您的lsh_read_line（）函数将始终为您返回具有不同文本的相同缓冲区。 然后，将指向此缓冲区的指针存储到数组中的不同单元格中。 一旦将其输入到行变量中，就应该将文本复制到新分配的字符串中，并且以后只能使用此新副本。