Solved

# How would I compare two char arrays in an array of structs

Posted on 2007-12-02
840 Views
Hi experts, quick general question. How would I go about comparing to char arrays from an array of structs, and sorting the structs in the array accordingly? (In this case alphabetical order).

I have tried compare(), but I get an error telling me there is an error for request of member of the struct I am trying to access.

Thanks for the help!
0
Question by:pacman32689
• 5
• 3
• 3
• +1

LVL 13

Expert Comment

ID: 20392236
A struct is the same as a class, except that a struct's data is public by default.  So a struct can contain methods.

I suggest a comparison method which is a member of the struct.  The comparison method would take a char array and compare to the char array which is also a member of the struct.
0

Author Comment

ID: 20392237
here was my initial attempt
``````if( contact[i+1].name.compare(contact.name[i]) == -1)
``````
0

LVL 55

Expert Comment

ID: 20392241
strcmp() will do the job, but the sorting algorithm is another story. I will elaborate in a moment.
0

LVL 53

Assisted Solution

Infinity08 earned 100 total points
ID: 20392245
You can use the STL sort :

http://www.cplusplus.com/reference/algorithm/sort.html

Something like :

``````#include <algorithm>

#include <string.h>

using namespace std;

struct MyStruct {

// ...

char name[16];

};

bool myStructCompare(MyStruct a, MyStruct b) {

return (strcmp(a.name, b.name) < 0);

}

int main(void) {

MyStruct array[10];

// fill the array ...

sort(&(array[0]), &(array[9]), myStructCompare);

return 0;

}
``````
0

LVL 55

Expert Comment

ID: 20392247
qsort() will be the shortest method. first define a comparison function, there you will use the strcmp() function:

#include <stdlib.h>
int comparefn(const void *a, consr void *b){
return strcmp((struct yourstruct *)a)->name, ((struct yourstruct *)b)->name);
}

then you can use qsort, using the new function as a callback:
qsort(arrayOfStruct,sizeof(arrayOfStruct)/sizeof(structType),sizeof(structType),comparefn);
0

LVL 55

Expert Comment

ID: 20392258
using your code of previous questions, should be:

#include <stdlib.h>
int comparefn(const void *a, consr void *b){
return strcmp((struct yourstruct *)a)->name, ((struct yourstruct *)b)->name);
}

then you can use qsort, using the new function as a callback:
qsort(contact,sizeof(contact)/sizeof(struct contactParameter),sizeof(struct contactParameter),comparefn);

notice my solution uses directly the char arrays (name), and doesn't require STL functions.
0

LVL 53

Expert Comment

ID: 20392267
>> and doesn't require STL functions.

You say that like it's a bad thing. It's not ... STL is the standard template library, and is part of C++ ... not using it is passing up on a great tool.
0

LVL 55

Expert Comment

ID: 20392274
I would suggest to use STL functions, if the struct has STL objects, but it is not the case.
I always try to avoid mixing libraries as far as possible.
0

Author Comment

ID: 20392279
Would this not work?
`````` strcmp(contact.name[i],contact.name[i+1])
``````
0

LVL 55

Accepted Solution

Jaime Olivares earned 150 total points
ID: 20392284
I think you mean:
strcmp(contact[i].name,contact[i+1].name)
is it?
0

Author Comment

ID: 20392287
Yes, thanks so much, it compiled!
0

LVL 53

Expert Comment

ID: 20392289
>> Would this not work?

If name is an array of strings, yes, but I suspect that name is a string (array of characters), so you just do :

strcmp(contact[i].name, contact[i+1].name)

to compare the name of contact i with the name of contact i + 1.
0

## Featured Post

Errors will happen. It is a fact of life for the programmer. How and when errors are detected have a great impact on quality and cost of a product. It is better to detect errors at compile time, when possible and practical. Errors that make their waâ€¦
Introduction This article is a continuation of the C/C++ Visual Studio Express debugger series. Part 1 provided a quick start guide in using the debugger. Part 2 focused on additional topics in breakpoints. As your assignments become a little more â€¦
The viewer will learn how to pass data into a function in C++. This is one step further in using functions. Instead of only printing text onto the console, the function will be able to perform calculations with argumentents given by the user.
The viewer will be introduced to the technique of using vectors in C++. The video will cover how to define a vector, store values in the vector and retrieve data from the values stored in the vector.