C-将命令行参数存储为Char数组

Question

If I have these two command line arguments, is there a way that I can take the second command line argument which is a single word containing 26 characters, separate all the letters and put them into a new array of characters?

./substitution qwertyuiopasdfghjklzxcvbnm

I tried using this syntax but I'm not sure if it is valid?

char mapping[] = argv[1];

I thought that this statement would create a new array of characters called mapping, and assign it to a string since I'm assuming argv[1] is a string. Then each index would have the respective characters as per the command line argument:

mapping[0] = 'q'
mapping[1] = 'w'
...

Any tips would be appreciated! :)

Answer 1

you cant assign value to an array like that. but instead you can use pointers. argv is an array of pointers to null terminated strings. which means they has the character '\\0' with ASCII value of zero at the end.

char *mapping = argv[1];

now mapping points to the first argument. and if you need a copy of the first arg you should allocate enough memory for the string with malloc ( stdlib.h ) function and then copy it to that block of memory with strcpy ( string.h ).

char *mapping = malloc(strlen(argv[1]) + 1); //strlen returns the size of the string not including the null character at the end.
strcpy(mapping,argv[1]);
...
free(mapping);//then you will have to free the allocated space when you are done with it.

now mapping is copy of argv[1] and modifying it wont affect argc[1] .