Realloc问题

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==============================================

有人能解释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：

它在realloc之后从start中删除“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

char*urlEncode（char*c）
{
#ifdef EBUG
printf（“urlEncode:编码“%s”\n”，c）；
#恩迪夫
int len=strlen（c）+1；
char*ret=malloc（sizeof（char）*len）；
memset（ret，0，len）；
int z=0；
char*escapee=malloc（sizeof（char）*4）；
逃犯[0]='%'；逃犯[3]='\0'；
for（int i=0；i=len）
{
ret=带端（ret，“”）；
len+=strlen（“”）；
}
printf（“z=%i len=%i ret=%s\n”，z，len，ret）；
if（（48realloc

的第一个参数必须是以前由

malloc

、

calloc

或

realloc

返回的指针，而不是随后的

free

d

如果不是这样，任何事情都可能发生，包括你所看到的

从哪里开始

来自哪里

---

编辑：发布您的编辑后，您似乎没有遇到realloc问题！

我认为您试图做的是包含两个字符串start和app，如果是这种情况，您最好使用strncat函数

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

#包括
char*strncat（char*str1，const char*str2，size\u t count）；

既然您原来的realloc问题似乎无法重现，我敢发布一个稍微经过重构的代码来满足您的要求。它在字符串上传递了两次，但在我看来，就执行的内存分配调用数量而言，它应该具有更可预测的性能—仅一次。它也是一个bi它不比你的短

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

int is_printable(char c) {
 return (48 <= c && c <= 57) ||//0-9
        (65 <= c && c <= 90) ||//abc...xyz
        (97 <= c && c <= 122) || //ABC...XYZ
        c == '~' || c =='!' || c== '*' ||
        c == '(' || c== ')' || c== '\'';
}

char *urlEncode(char *s) {
  char *ret, *c, *ct;
  int i, len;
  printf("urlEncode: Encoding '%s'\n", s);
  /* First pass - figure out how long the target string should be */
  len = 0;
  for(c=s; *c; c++) {
    if(is_printable(*c)) len++; else len += 3;
  }
  /* Don't forget we need to store terminating zero too */
  len++;
  printf("Current len: %d, target len: %d\n", strlen(s)+1, len);
  ct = ret = malloc(len);
  /* Second pass - copy/encode */
  for(c=s; *c; c++) {
    if(is_printable(*c)) {
      *ct++ = *c;
    } else {
      snprintf(ct, 4, "%%%02x", *c);
      ct += 3;
    }
  }
  *ct = 0; /* null-terminate the string */
  printf("Encoded string: %s\n", ret);
  return ret;
}

int main(int argc, char *argv[])
{
  urlEncode("testing encrypt");
  exit(1);
}

#包括
#包括
#包括
int可打印（字符c）{
返回（48
在我的系统中，分配的字符串newstr的地址等于start，不管“start”的分配大小是多少，很可能当它增长时，系统正在重新分配相同的内存位置
你能发布调用代码吗？特别是，start从何而来？IIRC sizeof（char）始终为1。我希望您通过执行
realloc（开始…）
，start可能会变成无效指针。您的新输出完全不同，并且似乎没有遇到您之前发布的问题？@Charles：是的。我无法解释。我正在尝试找出更多的东西。这很奇怪，我没有更改任何我不认为的内容……对，但我想处理内存管理和在函数内部增加str1，而不是在我调用strncatI之前。strncat不明白你的意思，strncat会为你增加字符串。strncat不会增加底层内存区域。它只会在第一个字符串后附加第二个字符串，并依赖调用方为其提供适当的限制以防止任何缓冲区溢出。“destination-指向目标数组的指针，该数组应该包含一个C字符串，并且足够大，可以包含连接的结果字符串，包括额外的空字符。”谢谢，这样更好。但是有一个小错误：它似乎翻转了编码值：“encoded string:testing%02encrypt”“不是%20，谢谢。格式字符串是错误的-它没有翻转部件，它总是打印%02:）“man snprintf”是我的朋友…不完全正确。第一个参数可能是
NULL
。
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int is_printable(char c) {
 return (48 <= c && c <= 57) ||//0-9
        (65 <= c && c <= 90) ||//abc...xyz
        (97 <= c && c <= 122) || //ABC...XYZ
        c == '~' || c =='!' || c== '*' ||
        c == '(' || c== ')' || c== '\'';
}

char *urlEncode(char *s) {
  char *ret, *c, *ct;
  int i, len;
  printf("urlEncode: Encoding '%s'\n", s);
  /* First pass - figure out how long the target string should be */
  len = 0;
  for(c=s; *c; c++) {
    if(is_printable(*c)) len++; else len += 3;
  }
  /* Don't forget we need to store terminating zero too */
  len++;
  printf("Current len: %d, target len: %d\n", strlen(s)+1, len);
  ct = ret = malloc(len);
  /* Second pass - copy/encode */
  for(c=s; *c; c++) {
    if(is_printable(*c)) {
      *ct++ = *c;
    } else {
      snprintf(ct, 4, "%%%02x", *c);
      ct += 3;
    }
  }
  *ct = 0; /* null-terminate the string */
  printf("Encoded string: %s\n", ret);
  return ret;
}

int main(int argc, char *argv[])
{
  urlEncode("testing encrypt");
  exit(1);
}

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 =(void*) realloc(start, sizeof(char) * (i + strlen(app) + 1));


  memset(newstr,'z',sizeof(char) * (i + strlen(app) + 1));
  printf("addres  %x\n",newstr);

  printf("after realloc: %s\n", newstr);
  while(app[j] != '\0')
    newstr[i++] = app[j++];

    //missing null terminating character
    newstr[i]=0;

  printf("strlen(newstr): %i\n", strlen(newstr));
  printf("newstr: %s\n", newstr);
  return newstr; 
  }