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我正在寫一個計算器從C從頭開始（家庭作業），並有內存的地方麻煩..算法完美，但我得到一組Valgrind錯誤/警告，例如：在C計算器memcheck的問題
echo -n「1」|的valgrind ./a.out --track-起源=是
==14261== Conditional jump or move depends on uninitialised value(s)
==14261== at 0x400B9F: create_rpn (main.c:53)
==14261== by 0x400742: main (main.c:253)
我生成文件：
all:
gcc main.c -g -O2 -Wall -Werror -std=c99
我的源代碼是下面(and on GitHub)。你能幫忙嗎？先謝謝你！
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_LEN 1024
// needs to check priority
int get_power(char op) {
if (op == '+') {
return 2;
} else if (op == '-') {
return 2;
} else if (op == '*') {
return 4;
} else if (op == '/') {
return 4;
} else {
return 0;
}
}
// checks if current char is operator
int is_operator(char op) {
if (op == '+' || op == '-' || op == '*' || op == '/') {
return 1;
} else {
return 0;
}
}
// checks if current char is digit
int is_digit(char op) {
if ((op >= '0' && op <= '9') || op == '.') {
return 1;
} else {
return 0;
}
}
// evaulates array in Postfix
double evaulate_rpn(char** exp, size_t len) {
double* stack = (double*) malloc(len*sizeof(double)); // stack for operands
double a1 = 0.0;
double a2 = 0.0; // buffers to save stack items
size_t place = 0; // current stack size
for (size_t i = 0; i < len; ++i) {
if (is_operator(*exp[i]) == 1) {
// takes out last 2 operands, processes
if (place > 1) {
a1 = stack[place - 2];
a2 = stack[place - 1];
if (strncmp(exp[i], "+", 1) == 0) {
stack[place - 2] = a1 + a2;
} else if (strncmp(exp[i], "-", 1) == 0) {
stack[place - 2] = a1 - a2;
} else if (strncmp(exp[i], "*", 1) == 0) {
stack[place - 2] = a1 * a2;
} else if (strncmp(exp[i], "/", 1) == 0) {
stack[place - 2] = a1/a2;
}
place -= 1;
} else if (place == 1) {
// unary minus, unary plus..
a1 = stack[place - 1];
if (strncmp(exp[i], "-", 1) == 0) {
stack[place - 1] = 0 - a1;
} else if (strncmp(exp[i], "+", 1) == 0) {
stack[place - 1] = a1;
}
} else {
// wrong order/anything else
printf("[error]");
exit(0);
}
} else {
// is operand -> convert char to double -> save double to stack
stack[place] = atof(exp[i]);
place++ ;
}
}
float res = stack[0];
free(stack);
return res; // result here
}
void push_to_stack(char*** reverse, size_t* inited_lines, size_t* used_lines, char* item, size_t size) {
if(*inited_lines <= *used_lines){
*inited_lines *= 2;
char** buf = (char**) realloc(*reverse, (*inited_lines)*sizeof(char**));
if (buf) {
*reverse = buf;
} else {
printf("[error]");
exit(0);
}
}
char* str = calloc(size + 1, sizeof(char));
if (str) {
memcpy(str, item, size + 1);
str[size] = '\0';
(*reverse)[*used_lines] = str;
(*used_lines)++ ;
} else {
printf("[error]");
exit(0);
}
}
// transform from Infix to Postfix notation
double create_rpn(char* exp, size_t len){
// stack of chars for operands()+-*/
char* stack = (char*) malloc(len);
if (stack == NULL) {
printf("[error]");
exit(0);
}
size_t stack_top = 0; // position of last item in stack
// array of numbers
size_t inited_lines = 1;
size_t used_lines = 0;
char** reverse = (char**) malloc(inited_lines*sizeof(char*));
if (reverse == NULL) {
printf("[error]");
exit(0);
}
char buffer = 0;
int bracket_deep = 0;
int digit = 0; // flag to start parsing Numbers/digits
size_t start_index = 0; // for parsing Long-Vals
size_t index = 0;
while (index <= len) {
buffer = exp[index]; // buffer constats only 1 char but it is a string
if (is_digit(buffer) == 1) {
// save first digit place
if (digit == 0) {
start_index = index;
digit = 1;
}
} else {
// push to stack when Num is over
if (digit == 1) {
digit = 0;
size_t size = index - start_index; // size of str
push_to_stack(&reverse, &inited_lines, &used_lines, exp + start_index, size);
}
// push Operands + check priority
if (is_operator(buffer) == 1) {
size_t power = get_power(buffer);
for (int i = stack_top - 1; i >= 0; --i) {
if (stack[i] == '(') {
break;
}
if (get_power(stack[i]) >= power) {
push_to_stack(&reverse, &inited_lines, &used_lines, &stack[i], 1);
stack_top-- ;
}
}
// push current Operand to stack
stack[stack_top++ ] = buffer;
} else if (buffer == '(') {
stack[stack_top++ ] = buffer;
bracket_deep++ ;
} else if (buffer == ')') {
// push operands to result
bracket_deep-- ;
stack_top-- ; // if no, '' will be added to output
while (stack[stack_top] != '(') {
push_to_stack(&reverse, &inited_lines, &used_lines, &stack[stack_top], 1);
if (stack_top > 0) {
stack_top-- ;
} else {
break;
}
}
} else if (buffer == ' ' || buffer == '\n') {
// ignore this case
} else if (buffer == '\0') {
for (int i = stack_top - 1; i >= 0; --i) {
push_to_stack(&reverse, &inited_lines, &used_lines, &stack[i], 1);
}
stack_top = 0;
} else {
printf("[error]"); // - wrong char: '%s', %c\n", buffer, *buffer); // wrong char!
exit(0);
}
}
if (bracket_deep < 0) {
printf("[error]"); // wrong bracket expr
exit(0);
}
index++ ;
}
free(stack);
if (bracket_deep == 0) {
double res = evaulate_rpn(reverse, used_lines);
for (int i = 0; i < inited_lines; i++) {
free(reverse[i]);
}
free(reverse);
return res;
} else {
printf("[error]"); // wrong brackets
exit(0);
}
}
int main() {
char* expression = (char*) malloc(MAX_LEN*sizeof(char));
if (expression) {
size_t len = 0;
while (scanf("%c", &expression[len]) != -1) { // switch to getch ???
if (expression[len] != ' ') { // save everything except spaces
len++ ;
}
}
double result = create_rpn(expression, len);
printf("%.2f", result);
free(expression);
} else {
printf("[error]");
exit(0);
}
return 0;
}
不要[鑄造的malloc'（）的結果']（http://stackoverflow.com/a/605858/1983495） –