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Access Methods for Pointers and Arrays in C

Tech Apr 22 11

One-Dimensional Array

int values[5] = {10, 20, 30, 40, 50};

printf("Using array indexing: values[i]\n");
for (int idx = 0; idx < 5; idx++) {
    printf("%d ", values[idx]);
}
printf("\n");

printf("Using pointer arithmetic: *(values + i)\n");
for (int idx = 0; idx < 5; idx++) {
    printf("%d ", *(values + idx));
}
printf("\n");

Two-Dimensional Array

int matrix[3][5] = { {10, 20, 30, 40, 50}, {20, 30, 40, 50, 60}, {30, 40, 50, 60, 90} };

printf("Using double indexing: matrix[i][j]\n");
for (int row = 0; row < 3; row++) {
    for (int col = 0; col < 5; col++) {
        printf("%d ", matrix[row][col]);
    }
    printf("\n");
}

printf("Using pointer dereferencing: (*(matrix + i))[j]\n");
for (int row = 0; row < 3; row++) {
    for (int col = 0; col < 5; col++) {
        printf("%d ", (*(matrix + row))[col]);
    }
    printf("\n");
}

printf("Using row pointer arithmetic: *(matrix[i] + j)\n");
for (int row = 0; row < 3; row++) {
    for (int col = 0; col < 5; col++) {
        printf("%d ", *(matrix[row] + col));
    }
    printf("\n");
}

printf("Using double pointer arithmetic: *(*(matrix + i) + j)\n");
for (int row = 0; row < 3; row++) {
    for (int col = 0; col < 5; col++) {
        printf("%d ", *(*(matrix + row) + col));
    }
    printf("\n");
}

Basic Pointer to Array

int* ptr = values;

printf("Using pointer as array: ptr[i]\n");
for (int idx = 0; idx < 5; idx++) {
    printf("%d ", ptr[idx]);
}
printf("\n");

Array of Pointers

int* ptr_array[5] = { values, values + 1, values + 2, values + 3, values + 4 };

printf("Dereferencing pointer array elements: *ptr_array[i]\n");
for (int idx = 0; idx < 5; idx++) {
    printf("%d ", *ptr_array[idx]);
}
printf("\n");

printf("Using pointer arithmetic on first element: *(*ptr_array + i)\n");
for (int idx = 0; idx < 5; idx++) {
    printf("%d ", *(*ptr_array + idx));
}
printf("\n");

Pointer to One-Dimensional Array

int (*array_ptr)[5] = values;

printf("Dereferencing array pointer: (*array_ptr)[i]\n");
for (int idx = 0; idx < 5; idx++) {
    printf("%d ", (*array_ptr)[idx]);
}
printf("\n");

printf("Using pointer arithmetic on dereferenced pointer: *((*array_ptr) + i)\n");
for (int idx = 0; idx < 5; idx++) {
    printf("%d ", *((*array_ptr) + idx));
}
printf("\n");

Pointer to Two-Dimensional Array

int (*matrix_ptr[3])[5] = { matrix, matrix + 1, matrix + 2 };

printf("Accessing via array of array pointers: (*matrix_ptr[i])[j]\n");
for (int row = 0; row < 3; row++) {
    for (int col = 0; col < 5; col++) {
        printf("%d ", (*matrix_ptr[row])[col]);
    }
    printf("\n");
}

printf("Using pointer arithmetic with array pointers: *((*matrix_ptr[i]) + j)\n");
for (int row = 0; row < 3; row++) {
    for (int col = 0; col < 5; col++) {
        printf("%d ", *((*matrix_ptr[row]) + col));
    }
    printf("\n");
}

Complete Example Code

#include <stdio.h>

int main() {
    int values[5] = {10, 20, 30, 40, 50};
    int matrix[3][5] = { {10, 20, 30, 40, 50}, {20, 30, 40, 50, 60}, {30, 40, 50, 60, 90} };
    int* ptr = values;
    int* ptr_array[5] = { values, values + 1, values + 2, values + 3, values + 4 };
    int (*array_ptr)[5] = values;
    int (*matrix_ptr[3])[5] = { matrix, matrix + 1, matrix + 2 };

    printf("Using array indexing: values[i]\n");
    for (int idx = 0; idx < 5; idx++) {
        printf("%d ", values[idx]);
    }
    printf("\n");

    printf("Using pointer arithmetic: *(values + i)\n");
    for (int idx = 0; idx < 5; idx++) {
        printf("%d ", *(values + idx));
    }
    printf("\n");

    printf("Using double indexing: matrix[i][j]\n");
    for (int row = 0; row < 3; row++) {
        for (int col = 0; col < 5; col++) {
            printf("%d ", matrix[row][col]);
        }
        printf("\n");
    }

    printf("Using pointer dereferencing: (*(matrix + i))[j]\n");
    for (int row = 0; row < 3; row++) {
        for (int col = 0; col < 5; col++) {
            printf("%d ", (*(matrix + row))[col]);
        }
        printf("\n");
    }

    printf("Using row pointer arithmetic: *(matrix[i] + j)\n");
    for (int row = 0; row < 3; row++) {
        for (int col = 0; col < 5; col++) {
            printf("%d ", *(matrix[row] + col));
        }
        printf("\n");
    }

    printf("Using double pointer arithmetic: *(*(matrix + i) + j)\n");
    for (int row = 0; row < 3; row++) {
        for (int col = 0; col < 5; col++) {
            printf("%d ", *(*(matrix + row) + col));
        }
        printf("\n");
    }

    printf("Using pointer as array: ptr[i]\n");
    for (int idx = 0; idx < 5; idx++) {
        printf("%d ", ptr[idx]);
    }
    printf("\n");

    printf("Dereferencing pointer array elements: *ptr_array[i]\n");
    for (int idx = 0; idx < 5; idx++) {
        printf("%d ", *ptr_array[idx]);
    }
    printf("\n");

    printf("Using pointer arithmetic on first element: *(*ptr_array + i)\n");
    for (int idx = 0; idx < 5; idx++) {
        printf("%d ", *(*ptr_array + idx));
    }
    printf("\n");

    printf("Dereferencing array pointer: (*array_ptr)[i]\n");
    for (int idx = 0; idx < 5; idx++) {
        printf("%d ", (*array_ptr)[idx]);
    }
    printf("\n");

    printf("Using pointer arithmetic on dereferenced pointer: *((*array_ptr) + i)\n");
    for (int idx = 0; idx < 5; idx++) {
        printf("%d ", *((*array_ptr) + idx));
    }
    printf("\n");

    printf("Accessing via array of array pointers: (*matrix_ptr[i])[j]\n");
    for (int row = 0; row < 3; row++) {
        for (int col = 0; col < 5; col++) {
            printf("%d ", (*matrix_ptr[row])[col]);
        }
        printf("\n");
    }

    printf("Using pointer arithmetic with array pointers: *((*matrix_ptr[i]) + j)\n");
    for (int row = 0; row < 3; row++) {
        for (int col = 0; col < 5; col++) {
            printf("%d ", *((*matrix_ptr[row]) + col));
        }
        printf("\n");
    }

    return 0;
}
Tags: C ProgrammingPointersArraysMemory Access
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