CODEWITHSUNDEEP
carraysstringpointerschar
Trent W
Trent W

Reputation: 95

Splitting C char array into words

I am trying to split a given char array into separate strings. I am doing this by putting the address of each word into an array, and then getting the string from the address to print.

So I have updated my code but now the program freezes after printing the numArgs but before "test2." I don't understand why.

----------------old code-----------------------   
char* parseArgs(char* comPtr){
    char *args[100] = {0};
    char *token;
    int i = 0;
    token = strtok(comPtr, " ");
    while(token != NULL){
        args[i] = malloc(100);
        args[i] = &token;
        token = strtok(NULL, " ");
    }
    return *args;
}

char* args = parseArgs(comPtr);
int i = 0;
while(i < numArgs){
    printf("arg%d: %s\n",i,&args[i]);
    i++;
}
-----------------------end old code--------------------

------------------new code------------------------
int countArgs(char* comPtr){
    char *token;
    int i = 0;
    token = strtok(comPtr, " ");
    while(token != NULL){
        i++;
        token = strtok(NULL, " ");
    }
    return i;
}

char** parseArgs(char* comPtr){
    printf("test1");
    char** args = calloc(100, sizeof(char*));
    char* token;
    int i = 0;
    while(token = strtok(comPtr, " ")){
        args[i] = token;
    }
    printf("test2");
    return args;
}

printf("ComPtr: %s\n",comPtr);
char* path = "/bin/";
//int pid = fork(); //pid always 0 so using pid = 1 to test
//printf("PID:%d",pid);
int pid = 1;
printf("PID:%d",pid);
if(pid != 0){
    int numArgs = countArgs(comPtr);
    printf("test1");
    printf("NumArgs: %d\n",numArgs);
    printf("test2");
    char** args = parseArgs(comPtr);
    int i = 0;
    printf("test3");
    while(i < numArgs){
        printf("arg%d: %s\n",i,args[i]);
        printf("test4");
        i++;
    }
}
else{
    //waitpid();
}

Upvotes: 0

Views: 4021

Answers (3)

Daniel Fischer
Daniel Fischer

Reputation: 183978

The freeze is due to

int i = 0;
while(token = strtok(comPtr, " ")){
    args[i] = token;
}

where you repeatedly - in an infinite loop - find the first token in comPtr, token becomes &comPtr[0] in each iteration (unless the string starts with spaces), and that is assigned to args[i].

After the first call, all calls to strtok that shall find further tokens in the same string - if any - should have a NULL first argument.

Also, you should probably increment i in the loop, since presumably you don't want to overwrite args[0] with each new token.

Upvotes: 0

Tony Delroy
Tony Delroy

Reputation: 106246

You've lost track of where your memory is, your pointers are pointing etc.. If you want to return the list of pointers to tokens, you need something like this:

char** parseArgs(char* comPtr){
    char** p_args = calloc(100, sizeof(char*);
    int i = 0;
    char* token;
    while (token = strtok(comPtr, " "))
        p_args[i] = token;
    return p_args;
}

char** p_args = parseArgs(comPtr);
int i = 0;
while(i < numArgs)
{
    printf("arg%d: %s\n",i,p_args[i]);
    i++;
}
free(p_args);

I haven't tested it, but it should point you in the right direction. Have a careful think about how it differs from your program, and use a debugger and/or printf() statements in the code to print out addresses and see how it works (or debug it if necessary).

Upvotes: 2

Sankar Mani
Sankar Mani

Reputation: 178

Declare the pointer array 'char *args[100]' as global variable. In your program your are allocating memory to the local pointer and its life is within the function. so at the end of the function your pointer variable scope ends. Here there is memory leak too.

Upvotes: 0

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