分段故障解析C字符串成指针数组时 [英] Segmentation fault when parsing c string into pointer array

问题描述

该函数makearg应该计数的字的数量在字符数组，也向上打破每个字到一个指针数组自己点。
分段故障似乎是与函数strncpy功能的问题。

  INT makearg（char中[]，CHAR ***参数）;诠释主（）{  焦炭** ARGS =（字符**）（的malloc（100））;  字符*海峡=LS是一个-l文件;
  INT ARGC;
  ARGC = makearg（STR，＆安培;参数）;  的printf（％D的argc）;
  的printf（％C，'\\ 0'）;  INT I;
  对于（i = 0; I＆LT; ARGC，我++）{
    看跌期权（参数）;
    的printf（％C，\\ n）;
  }
  返回0;
}/////////////////////////////////////////INT makearg（char中[]，CHAR ***参数）{  INT ARGC = 0;
  INT charc = 0;
  INT wordstart = 0;  而（1）{
    如果（S [charc] =='\\ 0'）{
      函数strncpy（* ARGS [ARGC]，S + wordstart，charc  -  wordstart）;
      ARGS [ARGC] [（charc  -  wordstart）+ 1] ='\\ 0';      ARGC ++;
      打破;
  }  如果（S [charc] ==''）{
    函数strncpy（* ARGS [ARGC]，S + wordstart，charc  -  wordstart）;
    ARGS [ARGC] [（charc  -  wordstart）+ 1] ='\\ 0';    wordstart = charc + 1;
    ARGC ++;
    charc ++;
  }  其他{
    charc ++;
    }
  }
  返回ARGC;
}
 

解决方案

您分配指针的 ARGS 阵列空间，但你永远不为你想让你的字符串分配空间存储在其中，所以当你尝试存储在 makearg 的琴弦，你是跨preting任何随机的垃圾有一个指针，而不是要的工作。

另外，你只分配100的字节的的指针数组 - 目前还不清楚有多少
你期望的话，能够分裂，但的malloc 调用应该看起来可能更像

 的char ** ARGS =的malloc（MAX_WORDS * sizeof的（字符*））; / *不需要造型* /
 

然后按照一个循环做MAX_WORDS多个的malloc 调用，以初始化 ARGS 与有效的指针

The function makearg is supposed to count the number of words in a char array and also break each word up into their own spot in a pointer array. Segmentation fault seems to be a problem with the strncpy function.

int makearg(char s[], char ***args);

int main(){

  char **args = (char**)(malloc(100));

  char *str = "ls is a -l file";
  int argc;
  argc = makearg(str, &args);

  printf("%d", argc);
  printf("%c", '\0');

  int i;
  for(i = 0; i < argc; i++){
    puts(args);
    printf("%c", '\n');
  }
  return 0;
}

/////////////////////////////////////////

int makearg(char s[], char ***args){

  int argc = 0;
  int charc = 0;
  int wordstart = 0;

  while(1){
    if(s[charc] == '\0'){
      strncpy(*args[argc], s + wordstart, charc - wordstart);
      args[argc][(charc - wordstart) + 1] = '\0';

      argc++;
      break;
  }

  if(s[charc] == ' '){
    strncpy(*args[argc], s + wordstart, charc - wordstart);
    args[argc][(charc -  wordstart) + 1] = '\0';

    wordstart = charc + 1;
    argc++;
    charc++;
  }

  else{
    charc++;
    }
  }
  return argc;
}

解决方案

You allocated space for the args array of pointers, but you never allocate space for the strings you intend to store in them, so when you try to store the strings in makearg, you are interpreting whatever random garbage is there as a pointer, and that's not going to work.

Also, you only allocate 100 bytes for the pointer array -- it's not clear how many words you expect to be able to split, but the malloc call should probably look more like

char **args = malloc(MAX_WORDS * sizeof(char *));  /* no cast required */

then follow that with a loop to do MAX_WORDS more malloc calls, in order to initialize args with valid pointers.

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