#include <stdio.h>
void MyFunction(char* MyArray[])
{
int i;
for(i=0; i<10; i++)
{
MyArray="Meaningless Content";
printf("%s\n",MyArray); //This is where it works.
}
}
int main()
{
char* MyArray[10][50];
MyFunction(MyArray);
int i;
for(i=0; i<10; i++)
{
printf("%s\n",MyArray); //This is where it doesn't work.
}
return 0;
}
[Question] Array Parameters
Author
Hey, I have a question.
I wrote a small C program, but I'm having trouble with some concept here.
Please take a look at the code real fast.
I basically wanted to make MyArray, pass it into MyFunction which will
manipulate it, then use the new values in main.
I printed MyArray in MyFunction, it prints out fine.
I printed MyArray in main after I called MyFunction, and it prints out garbage. T_T
So I assume it has something to do with pointers?
Or arrays as parameters?
Help would be much appreciated ^_^
You want to pass by reference instead of by pointer.
//void MyFunction(char* MyArray)void MyFunction(char &MyArray)
There's two problems here:
You can fix both of these issues by changing your MyArray type to char* MyArray[10].
C, not C++ :) - besides, that wouldn't help.
- MyFunction does not know that the array you're passing in is multidimensional, and is instead treating the array as 1-dimensional, storing values contiguously.
- Your array char* MyArray[10][50] is confused: It appears that you're trying to reserve storage for the characters in the array ([50]), but having the array store char *s, instead of just chars.
You can fix both of these issues by changing your MyArray type to char* MyArray[10].
Quote:Original post by vaneger
You want to pass by reference instead of by pointer.
*** Source Snippet Removed ***
C, not C++ :) - besides, that wouldn't help.
It would also be totally wrong, because this:
void MyFunction(char &MyArray)
gets an argument which is a reference to a single byte.
void MyFunction(char &MyArray)
gets an argument which is a reference to a single byte.
char v1; // A characterchar* v2; // A pointer to characterchar v3[50] // Array of characterchar v4[10][50] // Two-dimesional array of characterchar* v5[10][50] // Two-dimesional array of pointer to characterYou can not assign a string to a raw character array like this
v4 = "Meaningless Content"
Even if the compiler will accept it, the = operator does not know how to copy the content of one array into another array.
You need to use a function like strcpy
strcpy(v4, "Meaningless Content");
The strcpy function will typically loop throught the string copying one character at a time
Author
[SOLVED]
Ah, I got it now.
I was trying to read a text file, seperate the lines into an array, manipulate
them, and save them as another file.
My problem was with the parameter. I needed to specify the size of the second
dimension [50].
Your suggestions did fix my example.
Here is the actual source code I had a problem with.
It's obviously incomplete, but now it doesn't have a problem reading the
text file into the array.
I'm trying to become more familiar with functions from the C Standard Library.
If you have any suggestions about this code, please feel free to contribute.
[Edited by - jmpeer on December 29, 2009 12:44:29 PM]
Ah, I got it now.
I was trying to read a text file, seperate the lines into an array, manipulate
them, and save them as another file.
My problem was with the parameter. I needed to specify the size of the second
dimension [50].
Your suggestions did fix my example.
Here is the actual source code I had a problem with.
It's obviously incomplete, but now it doesn't have a problem reading the
text file into the array.
I'm trying to become more familiar with functions from the C Standard Library.
If you have any suggestions about this code, please feel free to contribute.
#include <stdio.h>int GetNumLines(FILE* List) //return number of lines in txt file to make approproate array (char* Content) size{ char* Line[50]; int NumLines = 0; while(!feof(List)) { fscanf(List,"%s",Line); NumLines++; } rewind(List); return NumLines;}void GetContent(char* Content[][50], int NumLines, FILE* List) //reads each line into array{ char* Line[50]; int i; for(i=0; i<NumLines; i++) { fscanf(List,"%s",Line); strcpy(Content,Line); }}void SortContent(char* Content[][50], int NumLines) //sorts it alpha.{ NumLines--;//prevents index out of bounds. I'm using strcmp with index+1 int x, y; char* Temp[50]; for(x=0; x<NumLines; x++) { for(y=0; y<NumLines; y++) { if(strcmp(Content[y],Content[y+1])>0) { strcpy(Temp,Content[y+1]); strcpy(Content[y+1],Content[y]); strcpy(Content[y],Temp); } } }}void SaveContent(char* Content[][50], int NumLines, FILE* NewList){ int i; for(i=0; i<NumLines; i++) { fprintf(NewList,"%s\n",Content); }}int main(){ FILE* List = fopen("list.txt","r"); int NumLines = GetNumLines(List); char* Content[NumLines][50]; GetContent(Content,NumLines,List); fclose(List); SortContent(Content,NumLines); FILE* NewList = fopen("list-edited.txt","w"); SaveContent(Content,NumLines,NewList); fclose(NewList); return 0;}[Edited by - jmpeer on December 29, 2009 12:44:29 PM]
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