Question

I have the following code, and on line 68, I’m getting a format error.
stack.c:68: warning: format ‘%e’ expects type ‘float *’, but argument 3 has type ‘double *’

On the input push 4, it gets a segfault. Not sure if they’re related. Please help!

#include <stdio.h>
#include <stdlib.h>
#define OFFSET '0'
#define DIM1 7
#define DIM2 5
#define RES_SIZE 1000

//typedef double double;

typedef struct {
  double *contents;
  int maxSize;
  int top;
} stackT;

void StackInit(stackT *stackP, int maxSize) {
    double *newContents;
    newContents = (double *)malloc(sizeof(double)*maxSize);
    if (newContents == NULL) {
        fprintf(stderr, "Not enough memory.\n");
        exit(1);
    }

    stackP->contents = newContents;
    stackP->maxSize = maxSize;
    stackP->top = -1;
}

void StackDestroy(stackT *stackP) {
    free(stackP->contents);
    stackP->contents = NULL;
    stackP->maxSize = 0;
    stackP->top = -1;
}

int StackIsEmpty(stackT *stackP) { return stackP->top < 0; }

int StackIsFull(stackT *stackP) { return stackP->top >= stackP->maxSize-1; }

void StackPush(stackT *stackP, double element) {
    if(StackIsFull(stackP)) {
        fprintf(stderr, "Can't push element: stack is full.\n");
        exit(1);
    }
    stackP->contents[++stackP->top] = element;
}

double StackPop(stackT *stackP) {
    if(StackIsEmpty(stackP)) {
        fprintf(stderr, "Can't pop element: stack is empty.\n");
        exit(1);
    }
    return stackP->contents[stackP->top--];
}

void StackShow(stackT *stackP) {
    int i;
    printf("[ ");
    for (i = 0; i < stackP->top - 1; i++) {
        printf("%e, ", stackP->contents[i]);
    }
    printf("%e ]\n", stackP->contents[stackP->top - 1]);
}

double shell(char* s1, double arg) {
    printf(">   ");
    scanf("%s %f%*c", s1, &arg);
    return arg;
}

int main() {
    //char cmds[DIM1][DIM2] = {{"push"}, {"pop"}, {"add"}, {"ifeq"}, {"jump"}, {"print"}, {"dup"}};
    stackT res;
    StackInit(&res, RES_SIZE);
    char cmd[DIM2]; double arg = 0;
    arg = shell(cmd, arg);
    if (StringEqual(cmd, "push")) {
        StackPush(&res, arg);
        StackShow(&res);
    }
}

Answer 1

Just had a quick look on you code , I think after pushing the first element your stack top pointer is set to 0 .
Now in you StackShow() method you are accessing an invalid memory location from this line :

 printf("%e ]\n", stackP->contents[stackP->top - 1]); // accessing invalid location stackP->contents[-1] 

This is an off-by-one error for the array contents .