c - 重新分配问题

Question

感谢您的查看，请忽略 - 各种恶作剧正在发生，我正在尝试调试更多内容。

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谁能解释一下 realloc 的这种行为吗？

输出:

before realloc start: testing%20encryp
before realloc app: '          '
realloc size: 27
after realloc: testing%20e
strlen(newstr): 11
newstr: testing%20e

代码:

char * strAppend(char * start, char * app)
{
  int i=strlen(start);
  int j=0;
  printf("before realloc start: %s\n", start);
  printf("before realloc app: '%s'\n", app);
  printf("realloc size: %i\n", i+strlen(app)+1);
  char * newstr = realloc(start, sizeof(char) * (i + strlen(app) + 1));
  printf("after realloc: %s\n", newstr);
  while(app[j] != '\0')
    newstr[i++] = app[j++];
  printf("strlen(newstr): %i\n", strlen(newstr));
  printf("newstr: %s\n", newstr);
  return newstr; }

它在重新分配后从开始处删除“ncryp”；但这不应该发生......

编辑:更多代码，更多输出

char * urlEncode(char * c)
{
#ifdef EBUG
  printf("urlEncode: Encoding '%s'\n", c);
#endif
  int len = strlen(c)+1;
  char * ret = malloc(sizeof(char) * len);
  memset(ret, 0, len);
  int z=0;
  char * escapee = malloc(sizeof(char) * 4);
  escapee[0] = '%'; escapee[3] = '\0';
  for(int i=0;i<strlen(c);i++)
    {
      printf("z = %i len = %i ret = %s\n", z, len, ret);
      if(z >= len)
        {
          ret = strAppend(ret, "          ");
          len += strlen("          ");
        }
      printf("z = %i len = %i ret = %s\n", z, len, ret);
      if ( (48 <= c[i] && c[i] <= 57) ||//0-9
           (65 <= c[i] && c[i] <= 90) ||//abc...xyz
           (97 <= c[i] && c[i] <= 122) || //ABC...XYZ
           (c[i]=='~' || c[i]=='!' || c[i]=='*' || c[i]=='(' || c[i]==')' || c[i]=='\'')
           )
        {
          ret[z++] = c[i];
        }
      else
        {
          char2hex(c[i], escapee);
          ret = strAppend(ret, escapee);
          z += 3;
        }
    }
  ret[z] = '\0';
  free(escapee);
#ifdef EBUG
  printf("urlEncode: Encoded string to '%s'\n", c);
#endif
  return ret;
}




urlEncode: Encoding 'testing encrypt'
z = 0 len = 16 ret =
z = 0 len = 16 ret =
z = 1 len = 16 ret = t
z = 1 len = 16 ret = t
z = 2 len = 16 ret = te
z = 2 len = 16 ret = te
z = 3 len = 16 ret = tes
z = 3 len = 16 ret = tes
z = 4 len = 16 ret = test
z = 4 len = 16 ret = test
z = 5 len = 16 ret = testi
z = 5 len = 16 ret = testi
z = 6 len = 16 ret = testin
z = 6 len = 16 ret = testin
z = 7 len = 16 ret = testing
z = 7 len = 16 ret = testing
before realloc start: testing
before realloc app: '%20'
realloc size: 11
after realloc: testing
strlen(newstr): 10
newstr: testing%20
z = 10 len = 16 ret = testing%20
z = 10 len = 16 ret = testing%20
z = 11 len = 16 ret = testing%20e
z = 11 len = 16 ret = testing%20e
z = 12 len = 16 ret = testing%20en
z = 12 len = 16 ret = testing%20en
z = 13 len = 16 ret = testing%20enc
z = 13 len = 16 ret = testing%20enc
z = 14 len = 16 ret = testing%20encr
z = 14 len = 16 ret = testing%20encr
z = 15 len = 16 ret = testing%20encry
z = 15 len = 16 ret = testing%20encry
z = 16 len = 16 ret = testing%20encryp
before realloc start: testing%20encryp
before realloc app: '          '
realloc size: 27
after realloc: testing%20encryp
strlen(newstr): 26
newstr: testing%20encryp
z = 16 len = 26 ret = testing%20encryp

上次编辑:

我不知道现在发生了什么。使用和不使用调试标志的程序的不同运行会产生不同的输出。我将回到绘图板并使用 valgrind 查找内存错误。

Answer 1

我认为你想要做的是连接两个字符串start和app，如果是这种情况，你最好使用strcat函数

#include <cstring>
char *strncat( char *str1, const char *str2, size_t count );