Valgrind: недействительные чтения

Question

Я пишу следующую программу:

int main() { 
    long sLen = 0; 
    char ch, *str = (char *)malloc(sizeof(char)); 
    while((ch = getchar()) != '\n') 
    { 
     str[sLen] = ch; 
     str = (char *)realloc(str, (1 + (sLen++)) * sizeof(char)); 
    } 

    int length = strlen(str); 

    printf("Length of string: %d\n", length); 
    printf("Input string: \"%s\"\n", str); 
    sort(str); 
    printf("Sorted: \"%s\"\n", str); 
    printf("Number of permutation: %i\n", factorial(length)); 
    permute(str, 0, length); 
    free(str); 
    return 0; 
} 

void sort(char sorted_str[]) { 
    for (int i = 0; sorted_str[i+1]; ++i) 
     for (int j = i + 1; sorted_str[j]; ++j) 
      if (sorted_str[i] > sorted_str[j]) { 
       char tmp = sorted_str[i]; 
       sorted_str[i] = sorted_str[j]; 
       sorted_str[j] = tmp; 
      } 

} 

void permute(char *a, int i, int n) { 
    if (i == (n-1)) printf("%s\n", a); 
    else { 
     for (int j = i; j < n; j++) { 
      swap((a+i), (a+j)); 
      permute(a, i+1, n); 
      swap((a+i), (a+j)); 
     } 
    } 
} 

И Valgrind дать мне это:

==20113== Invalid read of size 1 
==20113== at 0x4C294F4: strlen (mc_replace_strmem.c:390) 
==20113== by 0x400749: main (main.c:23) 
==20113== Address 0x51ba091 is 0 bytes after a block of size 1 alloc'd 
==20113== at 0x4C28CCE: realloc (vg_replace_malloc.c:632) 
==20113== by 0x40072B: main (main.c:19) 
==20113== Invalid read of size 1 
==20113== at 0x4E749EA: vfprintf (vfprintf.c:1623) 
==20113== by 0x4E7D1A9: printf (printf.c:35) 
==20113== by 0x400776: main (main.c:26) 
==20113== Address 0x51ba091 is 0 bytes after a block of size 1 alloc'd 
==20113== at 0x4C28CCE: realloc (vg_replace_malloc.c:632) 
==20113== by 0x40072B: main (main.c:19) 
==20113== Invalid read of size 1 
==20113== at 0x400893: sort (main.c:36) 
==20113== by 0x400782: main (main.c:27) 
==20113== Address 0x51ba091 is 0 bytes after a block of size 1 alloc'd 
==20113== at 0x4C28CCE: realloc (vg_replace_malloc.c:632) 
==20113== by 0x40072B: main (main.c:19) 
==20113== Invalid read of size 1 
==20113== at 0x4E749EA: vfprintf (vfprintf.c:1623) 
==20113== by 0x4E7D1A9: printf (printf.c:35) 
==20113== by 0x400798: main (main.c:28) 
==20113== Address 0x51ba091 is 0 bytes after a block of size 1 alloc'd 
==20113== at 0x4C28CCE: realloc (vg_replace_malloc.c:632) 
==20113== by 0x40072B: main (main.c:19) 
==20113== Invalid read of size 1 
==20113== at 0x4C29514: __GI_strlen (mc_replace_strmem.c:391) 
==20113== by 0x4E98DAA: puts (ioputs.c:37) 
==20113== by 0x4008C8: permute (main.c:47) 
==20113== by 0x4007C7: main (main.c:30) 
==20113== Address 0x51ba091 is 0 bytes after a block of size 1 alloc'd 
==20113== at 0x4C28CCE: realloc (vg_replace_malloc.c:632) 
==20113== by 0x40072B: main (main.c:19) 
==20113== HEAP SUMMARY: 
==20113==  in use at exit: 0 bytes in 0 blocks 
==20113== total heap usage: 2 allocs, 2 frees, 2 bytes allocated 
==20113== All heap blocks were freed -- no leaks are possible 
==20113== For counts of detected and suppressed errors, rerun with: -v 
==20113== ERROR SUMMARY: 5 errors from 5 contexts (suppressed: 4 from 4) 

Может кто-нибудь помочь с этим? Он работает, но я хочу иметь правильный код. Мой ввод a. Программа работает с этим, но valgrind дает мне эти 5 ошибок. Я знаю, что моя ошибка - это чтение из памяти, что valgrind не нравится, но я не могу найти это место в коде.

Answer 1

long sLen = 0; 
int ch; /* getchar() wants an int (not a a char) */ 
char *str = malloc(1); /* sizeof(char) is always 1, and don't cast malloc */ 
/* check the result of malloc */ 
if (str == NULL) { 
    perror("malloc"); 
    exit(EXIT_FAILURE); 
} 
while ((ch = getchar()) != '\n') 
{ 
    str[sLen] = ch; 
    str = realloc(str, 1 + ++sLen); // use ++sLen in order to get enough space 
    /* check the result of realloc */ 
    if (str == NULL) { 
     perror("realloc"); 
     exit(EXIT_FAILURE); 
    } 
} 
/* this is redundant, use sLen */ 
/* int length = strlen(str); */ 
int length = sLen; 
/* NUL-terminate the string */ 
str[sLen] = '\0'; 

С другой стороны:

for (int i = 0; sorted_str[i+1]; ++i) 

Это опасно (вы читаете вне границ массива, если sorted_str пуст), изменение к:

for (int i = 0; sorted_str[i] && sorted_str[i+1]; ++i)