C-字符串数组和神秘的Valgrind错误
[英]C - Array of Strings & Mysterious Valgrind Error
问题描述
I'm trying to allocate a two-dimensional array of strings, where the last member is always a NULL pointer, ie an empty array consists of a single NULL pointer. 
我正在尝试分配一个二维字符串数组，其中最后一个成员始终是NULL指针，即，一个空数组由一个NULL指针组成。 I keep getting Valgrind errors but I have no idea why. 我不断收到Valgrind错误，但我不知道为什么。
/*Initializes the string array to contain the initial
* NULL pointer, but nothing else.
* Returns: pointer to the array of strings that has one element
* (that contains NULL)
*/
char **init_array(void)
{
char **array = malloc(sizeof(char *));
array[0] = NULL;
return array;
}
/* Releases the memory used by the strings.
*/
void free_strings(char **array)
{
int i = 0;
while(array[i] != NULL){
free(array[i]);
i++;
}
//free(array[i]);
free(array);
}
/* Add <string> to the end of array <array>.
* Returns: pointer to the array after the string has been added.
*/
char **add_string(char **array, const char *string)
{
int i = 0;
while(array[i] != NULL){
i++;
}
array = realloc(array, (i+1) * sizeof(char *));
char *a = malloc(strlen(string)+1);
array[i] = malloc(strlen(string)+1);
strcpy(a, string);
strcpy(array[i], a);
free(a);
return array;
}
Here's the Valgrind error: 这是Valgrind错误：
==375== Invalid read of size 8 ==375== at 0x402FCE: add_string (strarray.c:40) ==375== by 0x401855: test_add_string (test_source.c:58) ==375== by 0x405F90: srunner_run_all (in /tmc/test/test) ==375== by 0x4028B2: tmc_run_tests (tmc-check.c:122) ==375== by 0x40256A: main (test_source.c:194) ==375== Address 0x518df08 is 0 bytes after a block of size 8 alloc'd ==375== at 0x4C245E2: realloc (vg_replace_malloc.c:525) ==375== by 0x402FF4: add_string (strarray.c:43) ==375== by 0x401855: test_add_string (test_source.c:58) ==375== by 0x405F90: srunner_run_all (in /tmc/test/test) ==375== by 0x4028B2: tmc_run_tests (tmc-check.c:122) ==375== by 0x40256A: main (test_source.c:194) ==375== ==375== Invalid read of size 8 ==375== at 0x4018F7: test_add_string (test_source.c:70) ==375== by 0x405F90: srunner_run_all (in /tmc/test/test) ==375== by 0x4028B2: tmc_run_tests (tmc-check.c:122) ==375== by 0x40256A: main (test_source.c:194) ==375== Address 0x518e308
2 个解决方案
解决方案1
3 已采纳 2015-03-14 09:27:55
That's because you didn't add new NULL-terminator to the array add_string() . 那是因为您没有向数组add_string()添加新的NULL终止符。 So subsequent calls of add_array() fail to find end of array without going out of bounds. 因此，随后对add_array()调用无法找到数组的结尾而不会超出范围。
I think you need realloc with larger length: 我认为您需要重新分配更大的长度：
array = realloc(array, (i + 2) * sizeof(char *));
And then save NULL-terminator to array[i + 1] : 然后将NULL终止符保存到array[i + 1] ：
array[i + 1] = NULL;
Why didn't you try using linked lists for that? 您为什么不尝试使用链接列表呢？ I feel bad for realloc() per each add_string() 我为每个add_string() realloc()感到add_string()
解决方案2
1 2015-03-14 09:42:05
This function 该功能
char **add_string(char **array, const char *string)
{
int i = 0;
while(array[i] != NULL){
i++;
}
array = realloc(array, (i+1) * sizeof(char *));
char *a = malloc(strlen(string)+1);
array[i] = malloc(strlen(string)+1);
strcpy(a, string);
strcpy(array[i], a);
free(a);
return array;
}
is wrong. 是错的。 It does not add a new slot into the array and you do not set the last element to NULL. 它不会在阵列中添加新的插槽，并且您不会将最后一个元素设置为NULL。
The valid function can look like 有效功能可能看起来像
char **add_string( char **array, const char *string )
{
int i = 0;
while ( array[i++] != NULL );
array = realloc( array, ( i + 1 ) * sizeof( char * ) );
array[i] = NULL;
array[i-1] = malloc( strlen( string ) + 1 );
strcpy( array[i-1], string );
return array;
}
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