Seg Fault using strcmp with * char

Question

I have this struct

typedef struct no
{
    char command[MAX_COMMAND_LINE_SIZE];
    struct no * prox;
} lista;

lista *listaCommand = NULL;

and I'm filling listaCommand with a simple function that seems to work ok, as I can read the values without any problem, but if I try to compare, like

strcmp(listaCommand->prox>command, ">")

I just get a segmentation fault, even though the value > is there, why this is happening?

Answer 1

strcmp(listaCommand->prox>command, ">") 

Should be

strcmp(listaCommand->prox->command, ">")

In your code listaCommand->prox>command will be seen as a comparison operation, using the > operator. A comparison in C returns an integer, 0 if false, non-zero otherwise. There are good chances it will return 0 , which is not a valid memory address. Hence, the segmentation fault.

Answer 2

Change

strcmp(listaCommand->prox>command, ">")

to

strcmp(listaCommand->prox->command, ">")

Answer 3

Allocate memory !!!

typedef struct no
{
    char str[20];
    struct no * prox;
} lista;

lista *listaCommand = NULL;

int main(int argc, char** argv)
{
    listaCommand = malloc(sizeof(lista));
    listaCommand->prox = malloc(sizeof(lista));
    strcpy(listaCommand->prox->str, "aaa");
    printf("%d\n", strcmp(listaCommand->prox->str, ">>"));

    free(listaCommand->prox);
    free(listaCommand);

    return 0;
}