C 中字符串从大写变为小写时堆溢出 [leetcode]

Question

当我运行此代码时，地址溢出。

=================================================================
==30==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x602000000036 at pc 0x55d8bdde3115 bp 0x7ffdf034bca0 sp 0x7ffdf034bc90
READ of size 1 at 0x602000000036 thread T0
    #3 0x7fa4f31310b2 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
0x602000000036 is located 0 bytes to the right of 6-byte region [0x602000000030,0x602000000036)
allocated by thread T0 here:
    #0 0x7fa4f3d76bc8 in malloc (/lib/x86_64-linux-gnu/libasan.so.5+0x10dbc8)
    #3 0x7fa4f31310b2 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
Shadow bytes around the buggy address:
  0x0c047fff7fb0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c047fff7fc0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c047fff7fd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c047fff7fe0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c047fff7ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c047fff8000: fa fa 06 fa fa fa[06]fa fa fa fa fa fa fa fa fa
  0x0c047fff8010: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8020: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8030: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8040: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8050: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07 
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
  Shadow gap:              cc
==30==ABORTING

我不明白为什么。

char* toLowerCase(char *str) {
  int len;
  int i;
  char newstr;
  len = strlen(str);
  //printf("Length of string = %d",len);
  newstr = (char*) malloc(len * sizeof(char) + 1);
  for (i = 0; i < len; i++) {
    if ((str[i] > 'a' && str[i] < 'z') || (str[i] > 'A' && str[i] < 'Z')) {
      if (str[i] > 'a' && str[i] < 'z') {
        newstr[i] = str[i];
        // printf("\n%c",newstr[i]);
      } else {
        newstr[i] = str[i] + 32;
      }
    } else {
      newstr[i] = str[i];
    }
  }
  return newstr;
}

Answer 1

用char newstr; 作为char *newstr; ;

newstr不指向字符串，因为目标缺少null 字符。 Append 一个。

  }
  newstr[i] = '\0'; // add
  return newstr;

调用代码在尝试打印字符串时肯定会失败。

---

旁白：下面在概念上是错误的，因为* sizeof(char)应该是len + 1 。

newstr = (char*) malloc(len * sizeof(char) + 1); // Poor

更好的是：（另请参阅Do I cast the result of malloc? ）

newstr = malloc(sizeof(char) * (len + 1)); // Good

由于sizeof(char)始终为 1，因此它以数字方式工作，但会是类型更广泛的错误。

对于char字符串，可以简化为以下内容。

newstr = malloc(len + 1); // Better

如果仍然想使用sizeof ，请使用引用数据的大小而不是尝试匹配类型。 这更容易正确编码、审查和维护。

newstr = malloc(sizeof *newstr * (len + 1)); // Recommended