CODEWITHSUNDEEP
cpointersmallocrealloc
tul1
tul1

Reputation: 414

Resizing Dynamic Matrix in C

I'm having troubles with something really silly. But I'm not been able to solve the problem. I designed a function that build a column matrix from a string resizing dynamically.

typedef struct{
double  ** m_;
size_t rows_, cols_;
}matrix_t;

int loadCol(char* str, matrix_t* col){
    size_t size=0; char* ptr;
    if(str==NULL)   return 0;
    if((col=(matrix_t*)malloc(sizeof(matrix_t)))==NULL) return 0;
    if((col->m_=(double**)malloc(sizeof(double*)))==NULL) return 0;
    ptr = strtok(str, "|");
    do{
        if(((col->m_)[0]=(double*)realloc((col->m_), sizeof(double)*(size+1)))==NULL){
            eraseMatrix(col); 
            return 0;
        }
        (col->m_)[0][size]=atof(ptr); /*SIGSEV*/
        size++;
    }while((ptr=strtok(NULL,"|"))!=NULL);
    col->cols_ = 1; col->rows_ = size;
    return size;
}

I debug with gdb and the problem seems to be in the assignment line mark with the comment SIGSEV. Also when the program's flow goes out from this function scope col->cols_ have incorrect data. Where is the problem in my function?

Upvotes: 0

Views: 76

Answers (1)

user3121023
user3121023

Reputation: 8286

For col to be modified in a function and the modifications reflected to the caller, a pointer to col needs to be passed as matrix_t **col. Then col has to be dereferenced in the function.
The caller would use loadCol ( str, &col); if col is declared as matrix_t *col = NULL;

int loadCol(char* str, matrix_t** col){
    size_t size=0; char* ptr;
    if(str==NULL)   return 0;
    if((*col=(matrix_t*)malloc(sizeof(matrix_t)))==NULL) return 0;
    if(((*col)->m_=(double**)malloc(sizeof(double*)))==NULL) return 0;
    ptr = strtok(str, "|");
    do{
        if((((*col)->m_)[0]=(double*)realloc(((*col)->m_)[0], sizeof(double)*(size+1)))==NULL){
            //eraseMatrix(col);
            return 0;
        }
        ((*col)->m_)[0][size]=atof(ptr);
        size++;
    }while((ptr=strtok(NULL,"|"))!=NULL);
    (*col)->cols_ = 1; (*col)->rows_ = size;
    return size;
}

strpbrk and strtod may also be used to parse values from the string.

int loadCol(char* str, matrix_t** col){
    size_t size=0; char* ptr;
    char *next = NULL;
    if(str==NULL)   return 0;
    if((*col=(matrix_t*)malloc(sizeof(matrix_t)))==NULL) return 0;
    if(((*col)->m_=(double**)malloc(sizeof(double*)))==NULL) return 0;
    next = str;
    while((ptr=strpbrk(next,"0123456789-+."))!=NULL) {
        if((((*col)->m_)[0]=(double*)realloc(((*col)->m_)[0], sizeof(double)*(size+1)))==NULL){
            //eraseMatrix(col);
            return 0;
        }
        ((*col)->m_)[0][size]=strtod(ptr,&next);
        size++;
    }
    (*col)->cols_ = 1; (*col)->rows_ = size;
    return size;
}

Upvotes: 1

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