Having problems with pointers and using strcmp() in C [duplicate] - c

Question

This question already has answers here:
Strcmp pointer from integer without cast
(4 answers)
Closed 7 years ago.
I'm writing a method that splits a given array into 2 parts. It keeps the first half in the original array and puts the other half into a temporary array using a symbol that marks where the split is. I'm getting erros as follows:
Warning: passing argument 2 of ‘strcmp’ makes pointer from integer without a cast
if(strcmp(input[i], symbol) == 0){
^
In file included from process.c:7:0:
/usr/include/string.h:144:12: note: expected ‘const char *’ but argument is of type ‘char’
extern int strcmp (const char *__s1, const char *__s2)
^
process.c:95:16: warning: assignment makes integer from pointer without a cast
input[i] = NULL;
^
process.c:96:26: warning: comparison between pointer and integer
while(input[i + 1] != NULL){
^
process.c:98:22: warning: assignment makes integer from pointer without a cast
input[i + 1] = NULL;
^
Here is my code:
char *splitCommands(char *input, char symbol){
int i = 0, j = 0;
char *temp;
int symbIndex; // where the symbol was
while(input[i] != NULL){
if(strcmp(input[i], symbol) == 0){
symbIndex = i;
input[i] = NULL;
while(input[i + 1] != NULL){
temp[j] = input[i + 1];
input[i + 1] = NULL;
i++;
j++;
}
break;
}
i++;
}
return temp;
}

Answer 1

You can directly do this comparison
if (input[i] == symbol)
because input[i] and symbol have type char and hence you compare their values, when the are strings you compare addresses which is why you need strcmp().
And
input[i + 1] = NULL;
is equivalent to
input[i + 1] = (void *) 0;
hence, you are trying to assign a pointer, to a char, which is also wrong, perhaps you mean
input[i + 1] = 0;
or in a more c-ish fashion
input[i + 1] = '\0';
Also, the while condition, the same problem, just
while (input[i])
would be enough, if you like your code to be more readable, I personally think that,
while (input[i] != '\0')
is more readable.
And you can't use temp like that because it's uninitialized, you need to allocate space for it, like this
temp = malloc(1 + estimatedSizeInBytes);
if (temp == NULL)
return NULL;
/* add the '\0' terminator */
temp[realSize - 1] = '\0';
where realSize <= estimatedSize.
You should also remember to free() the pointer returned by this function when you finish using it.

Answer 2

input[i] and symbol are char. So campare by imput[i] == symbol. And don't forget to allocate memory for char *tmp

Answer 3

There are several problems with your code but one of the primary problems and reason for your compiler errors is that strcmp() takes two pointers to c style strings as arguments. You are passing two char's to it, instead of pointers.
Another problem is that you're assigning a char to NULL, however NULL should only be used for pointers, not other types like char/int/float. If you're trying to check for the end of a c style string, check if the char is equal to 0 or '\0' instead. You'll probably have to spend more time learning about c style strings and pointers before you can finish this program.
I won't complete your assignment/work for you but I will give you an example of how to use strcmp():
#include <string.h>
#include <stdio.h>
int main()
{
char String1[4] = "abc";
char String2[4] = "xyz";
int Result = strcmp(String1, String2);
if (Result < 0)
printf("%s < %s\n", String1, String2);
if (Result == 0)
printf("%s = %s\n", String1, String2);
if (Result > 0)
printf("%s > %s\n", String1, String2);
return 0;
}
Output: abc < xyz
Here's an additional strcmp() reference from cplusplus.com.