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aruna1
Joined: 14 Oct 2008
Posts: 103
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| using string as a function parameter |
 Posted: Sun Dec 05, 2010 9:49 am |
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Hi guys can some one tell me how to use string as a input parameter to a function?
We can use single character as a input parameter but not a string of few characters.
Thank you.
Example:
| Code: |
void test (char string[5])
{
if string is "abcd" then do some thing
} |
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pmuldoon
Joined: 26 Sep 2003
Posts: 218
Location: Northern Indiana
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| Posted: Sun Dec 05, 2010 10:02 am |
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You can't pass a string to a function, but you can pass a pointer.
You can do something like:
| Code: |
char StrBuffer[20]; // allocate space for char array
strcpy(StrBuffer,"Hello World"); // copy a string into the array
test(StrBuffer); // pass the pointer to the array to the function
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and define test() as:
| Code: |
void test(char *String)
{
.
.
.
}
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Lookup strcpy() and strcmp() in the ccs manual. That should help. |
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aruna1
Joined: 14 Oct 2008
Posts: 103
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| Posted: Sun Dec 05, 2010 10:29 am |
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| pmuldoon wrote: | You can't pass a string to a function, but you can pass a pointer.
You can do something like:
| Code: |
char StrBuffer[20]; // allocate space for char array
strcpy(StrBuffer,"Hello World"); // copy a string into the array
test(StrBuffer); // pass the pointer to the array to the function
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and define test() as:
| Code: |
void test(char *String)
{
.
.
.
}
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Lookup strcpy() and strcmp() in the ccs manual. That should help. |
well how do they pass string ("hello world") to the strcpy function then? |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19506
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| Posted: Sun Dec 05, 2010 10:57 am |
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Start with a distinction. "Hello World", is technically a 'constant string'. A 'string' in C, is a null terminated array of characters. You can pass a function the pointer to a string array, as already outlined. In 'normal' C, a string constant, _is_ an array of characters, and you can pass the address of this, by just using it as a value in a function that accepts such an array. In CCS, there is a problem though, as a result of the program memory, and the data memory being separate, and on some chips not directly accessible. So CCS has a 'shortcut', that on such chips, if you take a function that accepts a single character as it's parameter, and call this with a constant string, the function is repeatedly called once, for each character in the string. On the older chips, CCS, effectively 'overloads' the strcpy function, and if it receives a RAM string, behaves normally, but if it receives a constant string, it accepts it character at a time, and appends these to the target, to simulate the normal behaviour...
On later chips that can address the ROM, the compiler accepts a special parameter 'PASS_STRINGS=IN_RAM'. If this is included in a device statement at the head of the program, the compiler will automatically detect the constant string, convert it to a RAM string for you, and pass the pointer as if this string was present in the RAM memory.
So provided your chip/compiler is modern, you can use:
| Code: |
//right near the top of your source
#device PASS_STRINGS=IN_RAM
void test (char *string) {
if (!strcmp(string,"abcd")) {
//do what you want;
}
}
test("bcde"); //This will execute the 'do what you want' code
test("abcd"); //This won't
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Best Wishes |
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aruna1
Joined: 14 Oct 2008
Posts: 103
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| Posted: Sun Dec 05, 2010 7:29 pm |
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hi Ttelmah
my compiler version is 4.084 and PIC is 16F877A |
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