问题
I have this c file
#include <stdio.h>
int main(int argc, char *argv[])
{
int x,i,sum;
sum = 0;
FILE *fin;
fin = fopen("testdata1", "r");
for (i = 0; i < 20; i++ ){
fscanf(fin, "%d", &x);
sum += x;
}
printf("Sum = %d", sum);
fclose(fin);
return 0;
}
I compiled it via gcc -ansi -pedantic -Wall app.c -o app
While compiling, I kept getting this warning error
warning: ISO C90 forbids mixing declarations and code [-Wdeclaration-after-statement] FILE *fin; ^ 1 warning generated.
Any hints on how do I stop that ?
回答1:
This is because in C89/C90, you have to first declare (eventually initialize) your variables, then put your code. Here is the highlighted problem:
int x,i,sum;
sum = 0; // This is code!
FILE *fin;
First solution is to initialize sum in the declaration:
int x,i,sum = 0;
Second solution is to initialize sum in the beginning of the code:
int x,i,sum;
FILE *fin;
sum = 0;
fin = fopen("testdata1", "r");
Third solution is to compile using another standard. With gcc/mingw, this is
achieved by passing the command-line option -std=<your standard>, for
example, -std=c99 or -std=c11 (and remove -ansi).
来源：https://stackoverflow.com/questions/42262965/warning-iso-c90-forbids-mixing-declarations-and-code-wdeclaration-after-state