CODEWITHSUNDEEP
cpointerscasting
Jordan
Jordan

Reputation: 2140

Double pointer to char[]

Alright, so I have the following code: 

char** args = (char**)malloc(10*sizeof(char*));
memset(args, 0, sizeof(char*)*10);

char* curToken = strtok(string, ";");

for (int z = 0; curToken != NULL; z++) {
    args[z] = strdup(curToken);
    curToken = strtok(NULL, ";")
}

I want every arg[z] casted into an array of chars -- char string[100] -- and then processed in the algorithms I have following. Every arg[z] needs to be casted to the variable string at some point. I am confused by pointers, but I am slowly getting better at them.

EDIT:

char string[100] = "ls ; date ; ls";

arg[0] will be ls, arg[1] will be date, and arg[2] will be ls after the above code.

I want to put each argument back into char string[100] and process it through algorithms.

Upvotes: 2

Views: 1351

Answers (3)

rashok
rashok

Reputation: 13434

one easiest way is to keep a backup of the original string in some temporary variable.

char string[100] = "ls ; date ; ls"; 
char temp_str[100] = {0};
strcpy (temp_str, string);

Another way is to do it by strcat. z has the number of agruments.

memset(string, '\0', 100);
for (i = 0; i < z; i++)
{
    strcat(string, args[i]);
    if (i != (z - 1))
    {
        //if it is last string dont append semicolon
        strcat(string, ";");
    }
}

Note : Take care of the boundary condition check

Upvotes: 1

unwind
unwind

Reputation: 399881

This:

char** args = (char**)malloc(10*sizeof(char*));
memset(args, 0, sizeof(char*)*10);

is broken code. First, you shouldn't cast malloc()'s return value. Second, args is a pointer to ten pointers to char. You can't set them to NULL using memset(), there's no guarantee that "all bytes zero" is the same as NULL. You need to use a loop.

Upvotes: 0

Martin Beckett
Martin Beckett

Reputation: 96119

If you want the parts of string copied into a fixed length string[100] then you need to malloc 100 chars for each args[] inside the loop and strncpy() the result of strtok into it. strdup will only allocate enough memory for the actual length of the supplied string (plus \0)

Upvotes: 0

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