c - 将函数返回的指针作为输入传递给其他函数时如何避免内存泄漏？

Question

我正在尝试编写一个简单的 C 矩阵库，它动态分配所需的内存并允许“嵌套”函数调用(如 fun1(fun2(x)))以避免执行长时间操作时声明过多的临时变量。但是，我无法摆脱因从未释放函数内部创建的结构而导致的内存泄漏。下面的例子清楚地表明了这一点。关于如何在不声明其他临时变量的情况下解决该问题的任何建议？

非常感谢

#include <stdio.h>
#include <stdlib.h>

struct _MatrixF{
    uint8_t rows;
    uint8_t cols;
    float* mat;
};
typedef struct _MatrixF* Matrix;

Matrix newMatrix(uint8_t rows, uint8_t cols){
    Matrix matrix = malloc(sizeof(struct _MatrixF));
    matrix->rows = rows;
    matrix->cols = cols;
    matrix->mat = malloc(rows * cols * sizeof(float));
    return matrix;
}

Matrix matIdentity(uint8_t rows, uint8_t cols){
    Matrix matrix = newMatrix(rows, cols);
    uint16_t ii;
    for (ii = 0; ii < (cols * rows); ii++)
        matrix->mat[ii] = (((ii / cols) == (ii % cols))? 1.0f : 0.0f);
    return matrix;
}


Matrix matAdd(Matrix lhs, Matrix rhs){
    Matrix m = newMatrix(lhs->rows, lhs->cols);
    uint16_t ii;
    for (ii = 0; ii < (lhs->cols * lhs->rows); ii++) {
        m->mat[ii] = lhs->mat[ii] + rhs->mat[ii];
    }
    return m;
}

Matrix matMult(Matrix lhs, Matrix rhs){
    uint8_t i, j, k;
    Matrix result = newMatrix(lhs->rows, rhs->cols);
    for (i=0; i < lhs->rows; i++)
        for (j=0; j < rhs->cols; j++)
            for (k=0; k < lhs->cols; k++)
                MAT(result, i, j) += MAT(lhs, i, k) * MAT(rhs, k, j);
    return result;
}

void mprint(Matrix m){
    printf("%dx%d\n", m->rows, m->cols);
    for(int i=0; i<m->rows; i++) {
        for (int j = 0; j<m->cols; j++)
            printf("%4.6f\t",(float) m->mat[(i) * m->cols + (j)]);
        printf("\n");
    }
}

int main(int argc, const char * argv[]) {
    Matrix A = matIdentity(4, 3);
    Matrix B = matIdentity(3, 2);
    Matrix C = matIdentity(2, 4);
    Matrix D = matIdentity(4, 4);
    uint16_t len = 64000;
    while (len--){
        Matrix E = matAdd(D, matAdd(D, matMult(matMult(A, B),C)));
        mprint(matMult(A, B));
        mprint(A);
        mprint(E);
    }
    return 0;
}

Answer 1

C 在自动处理这个问题上并没有提供多少帮助。您可以存储指向临时对象的指针，并在每次迭代结束时释放它们:

while (len--){
    Matrix t1, t2, t3, t4;
    Matrix E = matAdd(D, t1=matAdd(D, t2=matMult(t3=matMult(A, B),C)));
    mprint(t4=matMult(A, B));
    mprint(A);
    mprint(E);
    matFree(t1);
    matFree(t2);
    matFree(t3);
    matFree(t4);
}