c - 字符串/字符 * 连接，C

Question

我尝试打开一个文件(Myfile.txt)并将每一行连接到一个缓冲区，但得到了意外的输出。问题是，我的缓冲区没有更新最后连接的行。我的代码中缺少什么吗？

Myfile.txt(要打开和读取的文件)

Good morning line-001:
Good morning line-002:
Good morning line-003:
Good morning line-004:
Good morning line-005:
.
.
.

Mycode.c

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

int main(int argc, const char * argv[])
{
   /* Define a temporary variable */
   char Mybuff[100]; // (i dont want to fix this size, any option?)
   char *line = NULL;
   size_t len=0;
   FILE *fp;
   fp =fopen("Myfile.txt","r");
   if(fp==NULL)
   {
        printf("the file couldn't exist\n");
        return;
   }
   while (getline(&line, &len, fp) != -1 )
   {
       //Any function to concatinate the strings, here the "line"
       strcat(Mybuff,line);
   }
   fclose(fp);
   printf("Mybuff is: [%s]\n", Mybuff);

   return 0;
}

我期望我的输出是:

Mybuff is: [Good morning line-001:Good morning line-002:Good morning line-003:Good morning line-004:Good morning line-005:]

但是，我遇到了段错误(运行时错误)和垃圾值。有想做什么吗？谢谢。

Answer 1

指定MyBuff为指针，并使用动态内存分配。

#include <stdlib.h>    /*  for dynamic memory allocation functions */

char *MyBuff = calloc(1,1);    /* allocate one character, initialised to zero */
size_t length = 1;

while (getline(&line, &len, fp) != -1 )
{
     size_t newlength = length + strlen(line)
     char *temp = realloc(MyBuff, newlength);
     if (temp == NULL)
     {
          /*  Allocation failed.  Have a tantrum or take recovery action */
     }
     else
     {
          MyBuff = temp;
          length = newlength;
          strcat(MyBuff, temp);
     }
}

/*  Do whatever is needed with MyBuff */

free(MyBuff);

/*   Also, don't forget to release memory allocated by getline() */

上面的代码将为 getline() 读取的每一行在 MyBuff 中留下换行符。我将把删除它们作为练习。

注意:getline()是linux，而不是标准C。标准C中可以使用像fgets()这样的函数来从文件中读取行，尽管它不不像 getline() 那样分配内存。