strcpy char指针中止[关闭]

Question

我有这个代码：

     char **arr;
     char* line=NULL;
     int i=0;
     size_t len=0;
     ssize_t read1;

     fp=fopen("list.txt","r");
     if(fp==NULL)
         exit(EXIT_FAILURE);

     while((read1=getline(&line,&len,fp))!=-1)
         i++;
     fclose(fp);

     fp=fopen("list.txt","r");
     if(fp==NULL)
         exit(EXIT_FAILURE);

     arr=(char**)malloc(i*sizeof(char*)); // i is a variable i use to know the number of lines
     i=0;

     while((read1=getline(&line,&len,fp))!=-1)
     {
         line[strlen(line)]='\0';
         arr[i]=(char*)malloc(strlen(line)+1);
         strcpy(arr[i],line);
         i++;
     }

当我尝试strcpy 时程序崩溃。是malloc 问题吗？ 我很确定i 足够大。 line 最初是 char* 和 NULL。

编辑：我忘了这个程序是在 Qt 中的。

Answer 1

代码有几个问题，我会用我认为应该可行的方式发表评论...：

 // I **assume** that these are the definitions for these variables 
 // based on your comments
 size_t len = 0;
 char *line = NULL;
 ssize_t read1;

 // I **assume** that i has a reasonable value here, but this is not good to assume, 
 // what if the file is a line longer tomorrow? I hope that you calculate the number 
 // of lines somehow, that would be "less bad"
 int i = 10; // 10 lines in the file, who knows ?!?
 char **arr;

 // don't bother casting...
 arr = malloc(i * sizeof(char*)); 
 i=0;

 while((read1 = getline(&line, &len, fp)) != -1) {

     // THIS LINE DOES NOTHING, so we can just remove it
     // line[strlen(line)]='\0';

     arr[i] = line; // since you asked getline to allocate a buffer for 
                    // you (line was NULL), you can just store the buffer directly
                    // it's YOURS
     i++;

     // THIS IS THE BIG ONE:
     // it is needed because otherwise the NEXT call to getline will 
     // reuse the same buffer, which may not be big enough
     line = NULL;
 }

此外，稍后进行清理时，您应该执行以下操作：

int j;
for(j = 0; j < i; ++j) {
    free(arr[j]);
}
free(arr);
arr = NULL; // not necessary, but good practice to avoid double frees and such

Answer 2

你不测试你是否比原来的 i 有更多的行

 arr=(char**)malloc(i_ori*sizeof(char*));//i_ori is a variable i use to know the number of lines
 i=0;

 while((read1=getline(&line,&len,fp))!=-1 && i<i_ori)

此外，您永远不会测试 malloc 是否返回 NULL ！见https://stackoverflow.com/a/2280342/1458030

@Emil Grigore：当我尝试 strcpy 时，程序崩溃。是 malloc 问题？我很确定我足够大。

是的！您需要测试 NULL。

如果您使用 C++ 和 Qt，为什么不使用容器、流？