When using strcmp function (in the string.h library) , passing a 2-D character array as a parameter comparison , there is a need to add the ampersand symbol like
&mainlist[i][0]
otherwise like
mainlist[i][0]
there's an error
warning: passing argument 1 of 'strcmp' makes pointer from integer without a cast [-Wint-conversion]
versus when passing 1-D character array as a parameter comparison , its enough
mainlist[i]
without ampersand symbol. How come?
#include <stdio.h>
#include <string.h>
#define FOUND 1
#define NOT 0
int main()
{
char mainlist[5][10] = {"test1", "test2", "test3", "test4", "test5"};
int flag, i;
flag = NOT;
char myname[50];
printf("Enter ur name.\n");
scanf("%s", myname);
for(i = 0; i < 5; i++)
{
if(strcmp(mainlist[i], myname)== 0) //vs if(strcmp(&mainlist[i][0]), myname)==0)
{
flag = FOUND;
printf("Your name was found welcome.\n");
break;
}
}
if(flag == NOT)
{
printf("Your name was not found .\n");
}
}
When using strcmp function (in the string.h library) , passing a 2-D character array as a parameter comparison , there is a need to add the ampersand symbol like:
&mainlist[i][0]
Each use of an array index reduces a dimension of the array. mainlist is a 2D char array, mainlist[i] is a 1D char array, and mainlist[i][0] is a single char.
strcmp() requires its arguments to be pointers to the first char in the strings to compare, that's all that string are. mainlist[i][0] is a single char, like 't', so that won't work. &mainlist[i][0] is its address, a pointer to the first char in the string, so that works.
On the other hand, when you give an array is given as a function argument, what actually gets passed is a pointer to the first element of the array. For array mainlist[i], that's &mainlist[i][0]. Look familiar? This is presumably one of the key points you overlooked.
char mainlist[5][10] = {"test1", "test2", "test3", "test4", "test5"};
Looks like this in memory.
1 2 3 4
01234567890123456789012345678901234567890123456789
test1_____test2_____test3_____test4_____test5_____
^
|
mainlist
Where _ represents a null byte. mainlist points at the memory containing the first character.
When you ask for mainlist[i] that says to add i * 10 to the address of mainlist and dereference it. You can literally write *mainlist + i * 10
mainlist[1] mainlist[3]
| |
v v
1 2 3 4
01234567890123456789012345678901234567890123456789
test1_____test2_____test3_____test4_____test5_____
^ ^ ^
| | |
mainlist[0] mainlist[2] mainlist[4]
A pointer to the first character of a string is what a string is in C, a char *. Each of these are a string, a 1-D array, suitable for passing to strcmp.
mainlist[i][0] says to take the address of mainlist[i], add 0, and dereference it. The result is a char like t. This doesn't work with strcmp because it takes a pointer. The integer in "warning: passing argument 1 of 'strcmp' makes pointer from integer without a cast [-Wint-conversion]" is the char because characters are just integers and strcmp tried to use that integer as a char pointer.
&mainlist[i][0] says to make a pointer to that char, so we're back to a char * or mainlist[i].
mainlist[i] is almost always preferable to &mainlist[i][0]. However, it does have its uses. There are times when you want to skip the first few characters of a string, and you can do so without copying nor modifying the string.
For example, &mainlist[2][2] is "st3". It's a pointer to mainlist[2] + 2.
&mainlist[2][2]
|
v
01234567890123456789012345678901234567890123456789
test1_____test2_____test3_____test4_____test5_____
^
|
mainlist[2]
C will read from the pointer until the null byte.