c-分段故障和打印警告

Question

我的程序有一些警告，然后它崩溃了。事故似乎与警告有关，但我不理解。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 isn%st%dt%st%ft%c",W[0].name,W[0].id,
         W[0].department,W[1].res.gpa,W[0].res.grade);
    printf("nSecond student data isn%st%dt%st%ft%c",W[1].name,W[1].id,
         W[1].res.gpa,W[1].res.grade);
}

编译器在第二个printf:中打印了这些关于格式说明符的警告

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=]

当我尝试启动程序时，第一个printf打印了一行，但第二个失败了：

 Segmentation fault (core dumped)

它怎么了？如何修复警告和崩溃？

Answer 1

department缺少参数。很明显，当你编译打开警告(-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打印的W[1].res可能是W[0].res。

固定版本：

struct student W[] = {{"Saud Farooqui",137,"Electronics",{3.05,'A'}},
  {"Talha Farooqui",129,"Civil",{3.5,'A'}}};
printf("First student data isn%st%dt%st%ft%c",
    W[0].name, W[0].id, W[0].department, W[0].res.gpa, W[0].res.grade);
printf("nSecond student data isn%st%dt%st%ft%c",
    W[1].name, W[1].id, W[1].department, W[1].res.gpa, W[1].res.grade);

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