String manipulation is a fundamental aspect of C programming, and one common task is comparing strings. Whether you’re searching for a specific substring, sorting a list of names, or validating user inputs, string comparison is at the heart of many operations.
In C, two primary functions, strcmp() and strcmpi(), come into play when it comes to comparing strings, but they serve distinct purposes.
The strcmp() function is a stalwart for case-sensitive string comparisons. It meticulously examines every character within two strings, discerning even the slightest variations. On the other hand, the strcmpi() function offers a more relaxed approach, performing case-insensitive comparisons, where ‘A’ is equivalent to ‘a,’ and ‘B’ is equal to ‘b.’
In this article, we’ll delve into the intricacies of these two C library functions, comparing their strengths and weaknesses. We’ll explore their usage, behavior, and the scenarios in which one should be chosen over the other.
By the end, you’ll have a clear understanding of when to employ strcmp() and when strcmpi() is the better option for your string comparison needs. Let’s embark on this journey of understanding case-sensitive and case-insensitive string comparisons in the world of C programming.
The strcmp() Function in C
When comparing two strings, the strcmp() function takes into account case. Based on the ASCII value of each character, it compares strings character by character.
The syntax of strcmp() is:
int strcmp(const char *str1, const char *str2);
It returns:
- 0 if both strings are equal
- A negative number if str1 < str2
- A positive number if str1 > str2
Let’s look at an example:
#include <stdio.h>
#include <string.h>
int main() {
char str1[15] = "String1";
char str2[15] = "String2";
int result = strcmp(str1, str2);
if(result < 0) {
printf("str1 is less than str2\n");
}
else if(result > 0) {
printf("str1 is greater than str2\n");
}
else {
printf("str1 is equal to str2\n");
}
return 0;
}
Output:
str1 is less than str2
This prints “str1 is less than str2” as string comparison is case-sensitive.
Some key properties of strcmp():
- Comparison is case-sensitive
- ASCII values of characters are compared
- Useful for sorting, finding min/max strings etc.
The strcmpi() Function in C
The “string.h” header file contains the definition of the strcmpi() function, a built-in function in the C language. The only distinction between the strcmpi() and strcmp() functions is that the former is case sensitive while the latter is not, making strcmpi() identical to strcmp().
The syntax is:
int strcmpi(const char *str1, const char *str2);
This function accepts two string parameters to compare:
- str1 – The first string passed to the function. This will be compared against the second string.
- str2 – The second string passed to the function. This will be compared against the first string.
The function returns an integer value indicating the result of the comparison:
| Return Value | Meaning |
| 0 | str1 and str2 are identical |
| Negative number | str1 length < str2 length |
| Positive number | str1 length > str2 length |
Examples
| str1 | str2 | Return Value | Reason |
| “hello” | “hello” | 0 | Strings are identical |
| “cat” | “tiger” | -3 | “cat” length (3) < “tiger” length (5) |
| “antelope” | “deer” | 4 | “antelope” length (8) > “deer” length (4) |
Note: The strcmpi() function is a non-standard one that might not be found in the C standard library.
Let’s look at an example:
#include <stdio.h>
#include <string.h>
int main() {
char str1[15] = "String1";
char str2[15] = "string1";
int result = strcmpi(str1, str2);
if(result == 0) {
printf("str1 is equal to str2\n");
}
return 0;
}
Output:
str1 is equal to str2
This prints “str1 is equal to str2” as case is ignored by strcmpi().
Some key points about strcmpi():
- Comparison ignores upper/lower case differences
- Case is internally normalized before comparing
- Useful for comparing user input or configurations
Key Differences Between strcmp() and strcmpi() in C
| Feature | strcmp() | strcmpi() |
| Case sensitivity | Case-sensitive comparison | Case-insensitive comparison |
| Normalization | No normalization | Normalizes to same case before comparing |
| Comparison method | Directly compares ASCII values | Normalizes case, then compares ASCII values |
| Performance | Faster as direct comparison | Slower due to normalization |
| Return value | Negative if str1 < str2, Positive if str1 > str2, 0 if equal | 0 if equal, non-zero if unequal |
| Use cases | Sorting, finding min/max strings | User input validation, configuration value comparison |
When to Use Each Function
Based on their behavior, here are some guidelines on when to use each function:
- Use strcmp() when case matters, like for sorting or finding min/max
- Use strcmpi() when case must be ignored, like user input validation
- Use strcmp() for comparing identifiers, tokens, symbols etc.
- Use strcmpi() for comparing configuration values, file paths etc.
Conclusion
String comparison is fundamental to many C programs. Both strcmp() and strcmpi() allow for the comparison of two strings, with the main difference being that strcmpi() ignores case. Keeping their exact behavior in mind helps us choose the right function based on whether case-sensitivity matters for our specific use case.