C语言代码在在线编译器/CLion表现不稳定，VS运行异常求排查

问题现象 #

这段统计食品增减变动的代码在在线C编译器上运行完全正常，但在本地IDE中出现异常：

• CLion：首次运行输出正确，第二次、第三次输出错误值，后续又恢复正常
• Visual Studio：运行完全异常

已在多台设备和在线编译器验证过代码。

原代码如下：

typedef enum { kus=1,kg } Jednotka;
typedef union { int kus; float kg; } Mnozstvi;
typedef enum { rohlik,chleb,brambory,sirup,merunky,cukr,cokolada,salam,mleko,kava,pivo,mouka,maso,sul,kmin,fazole,meloun } Potravina;
typedef struct { Potravina potr; Jednotka jedn; Mnozstvi mnoz; } Pohyb;

const Pohyb pohyb[]={{chleb,kg,{.kg=20}},{cukr,kg,{.kg=10}},{rohlik,kus,{.kus=70}},{cokolada,kus,{.kus=15}},{kava,kg,{.kg=2}},{mouka,kg,{.kg=5}},
                     {salam,kg,{.kg=6.5}},{mleko,kus,{.kus=30}},{brambory,kg,{.kg=40}},{merunky,kg,{.kg=8}},{sirup,kus,{.kus=18}},{mouka,kg,{.kg=5}},
                     {cukr,kg,{.kg=-1.5}},{cokolada,kus,{.kus=-2}},{brambory,kg,{.kg=-5}},{rohlik,kus,{.kus=-10}},{pivo,kus,{.kus=10}},
                     {kmin,kg,{.kg=.06}},{fazole,kg,{.kg=5}},{chleb,kg,{.kg=-1}},{mleko,kus,{.kus=-2}},{sirup,kus,{.kus=-1}},{pivo,kus,{.kus=25}},
                     {kava,kg,{.kg=6.5}},{mouka,kg,{.kg=-4}},{fazole,kg,{.kg=-.5}},{cukr,kg,{.kg=-2}},{cokolada,kus,{.kus=-3}},{sul,kg,{.kg=6}},
                     {brambory,kg,{.kg=-3.5}},{merunky,kg,{.kg=-.5}},{sirup,kus,{.kus=-3}},{mouka,kg,{.kg=5}},{pivo,kus,{.kus=-1}},
                     {mouka,kg,{.kg=-2}},{maso,kg,{.kg=10}},{maso,kg,{.kg=5.5}},{rohlik,kus,{.kus=-4}},{chleb,kg,{.kg=-3}},{rohlik,kus,{.kus=-35}},
                     {sirup,kus,{.kus=5}},{cokolada,kus,{.kus=-2}},{salam,kg,{.kg=-.3}},{merunky,kg,{.kg=-3}},{maso,kg,{.kg=-.5}},{maso,kg,{.kg=-.8}},
                     {meloun,kg,{.kg=22.5}},{meloun,kg,{.kg=-3.2}},{chleb,kg,{.kg=-.5}},{sirup,kus,{.kus=-1}},{mleko,kus,{.kus=-4}},{sul,kg,{.kg=-1}},
                     {rohlik,kus,{.kus=20}},{maso,kg,{.kg=-1.5}},{pivo,kus,{.kus=-8}}};

const unsigned POHYB=sizeof pohyb/sizeof *pohyb;

const char *nazev[]={"rohlik","chleb","brambory","sirup","merunky","cukr","cokolada","salam","mleko","kava","pivo","mouka","maso","sul","kmin","fazole","meloun"};

#include <stdio.h>

int main() {
    int pocetPotravin = sizeof nazev / sizeof nazev[0]; // 17
    typedef struct {
        Potravina nazev;
        float myMnz;
        Jednotka myJedn;
    } vysPohyb;
    vysPohyb vyspohyb[pocetPotravin];
    for (int i = 0; i < pocetPotravin; ++i) {
        vyspohyb[i].nazev = i;
    }

    for (int i = 0; i < POHYB; ++i) {
        if (pohyb[i].jedn == 2) {
            vyspohyb[pohyb[i].potr].myMnz = vyspohyb[pohyb[i].potr].myMnz + pohyb[i].mnoz.kg;
            vyspohyb[pohyb[i].potr].myJedn = pohyb[i].jedn;
        }
        else {
            vyspohyb[pohyb[i].potr].myMnz = vyspohyb[pohyb[i].potr].myMnz + pohyb[i].mnoz.kus;
            vyspohyb[pohyb[i].potr].myJedn = pohyb[i].jedn;
        }
    }
    for (int i = 0; i < pocetPotravin; ++i) {
        if (vyspohyb[i].myJedn == 2) {
            printf("%s %g kg \n", nazev[vyspohyb[i].nazev], vyspohyb[i].myMnz);
        }
        else {
            printf("%s %g ks \n", nazev[vyspohyb[i].nazev], vyspohyb[i].myMnz);
        }
    }
}

问题根源 #

核心问题是未初始化局部结构体数组vyspohyb的myMnz和myJedn成员：

• 局部变量默认存储在栈内存中，栈内存的初始值是随机的垃圾数据
• 在线编译器每次运行都会重置栈环境，垃圾值恰好不影响计算结果；而本地IDE（如VS、CLion）的栈复用机制会导致多次运行时垃圾值不一致，出现时好时坏的异常
• 代码中仅初始化了nazev成员，myMnz（用于累加库存变动）和myJedn（存储单位）的初始值都是随机值，累加计算时会把垃圾值也包含进去，导致结果错误

修复方案 #

初始化vyspohyb数组的所有成员，将myMnz设为0（库存初始值为0），myJedn初始化为0（后续会被实际操作覆盖）。修复后的代码如下：

typedef enum { kus=1,kg } Jednotka;
typedef union { int kus; float kg; } Mnozstvi;
typedef enum { rohlik,chleb,brambory,sirup,merunky,cukr,cokolada,salam,mleko,kava,pivo,mouka,maso,sul,kmin,fazole,meloun } Potravina;
typedef struct { Potravina potr; Jednotka jedn; Mnozstvi mnoz; } Pohyb;

const Pohyb pohyb[]={{chleb,kg,{.kg=20}},{cukr,kg,{.kg=10}},{rohlik,kus,{.kus=70}},{cokolada,kus,{.kus=15}},{kava,kg,{.kg=2}},{mouka,kg,{.kg=5}},
                     {salam,kg,{.kg=6.5}},{mleko,kus,{.kus=30}},{brambory,kg,{.kg=40}},{merunky,kg,{.kg=8}},{sirup,kus,{.kus=18}},{mouka,kg,{.kg=5}},
                     {cukr,kg,{.kg=-1.5}},{cokolada,kus,{.kus=-2}},{brambory,kg,{.kg=-5}},{rohlik,kus,{.kus=-10}},{pivo,kus,{.kus=10}},
                     {kmin,kg,{.kg=.06}},{fazole,kg,{.kg=5}},{chleb,kg,{.kg=-1}},{mleko,kus,{.kus=-2}},{sirup,kus,{.kus=-1}},{pivo,kus,{.kus=25}},
                     {kava,kg,{.kg=6.5}},{mouka,kg,{.kg=-4}},{fazole,kg,{.kg=-.5}},{cukr,kg,{.kg=-2}},{cokolada,kus,{.kus=-3}},{sul,kg,{.kg=6}},
                     {brambory,kg,{.kg=-3.5}},{merunky,kg,{.kg=-.5}},{sirup,kus,{.kus=-3}},{mouka,kg,{.kg=5}},{pivo,kus,{.kus=-1}},
                     {mouka,kg,{.kg=-2}},{maso,kg,{.kg=10}},{maso,kg,{.kg=5.5}},{rohlik,kus,{.kus=-4}},{chleb,kg,{.kg=-3}},{rohlik,kus,{.kus=-35}},
                     {sirup,kus,{.kus=5}},{cokolada,kus,{.kus=-2}},{salam,kg,{.kg=-.3}},{merunky,kg,{.kg=-3}},{maso,kg,{.kg=-.5}},{maso,kg,{.kg=-.8}},
                     {meloun,kg,{.kg=22.5}},{meloun,kg,{.kg=-3.2}},{chleb,kg,{.kg=-.5}},{sirup,kus,{.kus=-1}},{mleko,kus,{.kus=-4}},{sul,kg,{.kg=-1}},
                     {rohlik,kus,{.kus=20}},{maso,kg,{.kg=-1.5}},{pivo,kus,{.kus=-8}}};

const unsigned POHYB=sizeof pohyb/sizeof *pohyb;

const char *nazev[]={"rohlik","chleb","brambory","sirup","merunky","cukr","cokolada","salam","mleko","kava","pivo","mouka","maso","sul","kmin","fazole","meloun"};

#include <stdio.h>

int main() {
    int pocetPotravin = sizeof nazev / sizeof nazev[0]; // 17
    typedef struct {
        Potravina nazev;
        float myMnz;
        Jednotka myJedn;
    } vysPohyb;
    vysPohyb vyspohyb[pocetPotravin];
    // 初始化所有成员：库存初始值设为0，单位初始化为0
    for (int i = 0; i < pocetPotravin; ++i) {
        vyspohyb[i].nazev = i;
        vyspohyb[i].myMnz = 0.0f;
        vyspohyb[i].myJedn = 0;
    }

    for (int i = 0; i < POHYB; ++i) {
        if (pohyb[i].jedn == kg) { // 用枚举常量替代魔法数字2，提升可读性
            vyspohyb[pohyb[i].potr].myMnz += pohyb[i].mnoz.kg;
            vyspohyb[pohyb[i].potr].myJedn = pohyb[i].jedn;
        }
        else {
            vyspohyb[pohyb[i].potr].myMnz += pohyb[i].mnoz.kus;
            vyspohyb[pohyb[i].potr].myJedn = pohyb[i].jedn;
        }
    }
    for (int i = 0; i < pocetPotravin; ++i) {
        if (vyspohyb[i].myJedn == kg) {
            printf("%s %g kg \n", nazev[vyspohyb[i].nazev], vyspohyb[i].myMnz);
        }
        else {
            printf("%s %g ks \n", nazev[vyspohyb[i].nazev], vyspohyb[i].myMnz);
        }
    }
    return 0;
}

额外优化说明 #

• 将判断条件中的魔法数字2替换为枚举常量kg，避免硬编码，提升代码可读性和维护性
• 使用+=运算符替代= a + b的写法，简化代码逻辑
• 增加return 0;语句，符合C标准中main函数的返回规范

内容的提问来源于stack exchange，提问作者dejvoos