c - 段错误和 printf 警告

Question

我的程序出现一些警告，然后崩溃了。崩溃似乎与警告有关，但我不明白它们。这是我的代码:

#include <stdio.h>

struct student {
    char name[100];
    int id;
    char *department;
    struct result {
        float gpa;
        char grade;
    } res;
};

int main(void) {
    struct student W[] = {{"Saud Farooqui",137,"Electronics",{3.05,'A'}},
          {"Talha Farooqui",129,"Civil",{3.5,'A'}}};

    printf("First student data is\n%s\t%d\t%s\t%f\t%c",W[0].name,W[0].id,
         W[0].department,W[1].res.gpa,W[0].res.grade);

    printf("\nSecond student data is\n%s\t%d\t%s\t%f\t%c",W[1].name,W[1].id,
         W[1].res.gpa,W[1].res.grade);
}

编译器在第二个 printf 中打印了有关格式说明符的这些警告:

foo.c:24:10: warning: format '%s' expects argument of type 'char *', but argument 4 has type 'double' [-Wformat=]
          W[1].res.gpa,W[1].res.grade);
          ^
foo.c:24:10: warning: format '%f' expects argument of type 'double', but argument 5 has type 'int' [-Wformat=]
foo.c:24:10: warning: format '%c' expects a matching 'int' argument [-Wformat=]

当我尝试启动该程序时，第一个 printf 打印了一行，但第二个失败了:

 Segmentation fault (core dumped)

这有什么问题吗？如何解决警告和崩溃问题？

Answer 1

department 缺少参数。很明显，当你编译时 打开警告(-Wall):

a.c:21:7: warning: format ‘%s’ expects argument of type ‘char *’, but argument 4 has type ‘double’ [-Wformat=]
       W[1].name, W[1].id,  W[1].res.gpa, W[1].res.grade);
       ^
a.c:21:7: warning: format ‘%f’ expects argument of type ‘double’, but argument 5 has type ‘int’ [-Wformat=]
a.c:21:7: warning: format ‘%c’ expects a matching ‘int’ argument [-Wformat=]

此外，您的第一个 printf 打印 W[1].res ，它可能应该是 W[0].res。

修复版本:

struct student W[] = {{"Saud Farooqui",137,"Electronics",{3.05,'A'}},
  {"Talha Farooqui",129,"Civil",{3.5,'A'}}};

printf("First student data is\n%s\t%d\t%s\t%f\t%c",
    W[0].name, W[0].id, W[0].department, W[0].res.gpa, W[0].res.grade);

printf("\nSecond student data is\n%s\t%d\t%s\t%f\t%c",
    W[1].name, W[1].id, W[1].department, W[1].res.gpa, W[1].res.grade);

因此，段错误是由于尝试将 W[1].res.gpa 解释为指向字符串的指针(对应于 %s 格式说明符) )，即 const char *。