c - Sprintf 函数 + 顺序参数

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我有两个具有特定值的字符串 ta 和 tb，然后我在编写时使用函数 sprintf 将这两个字符串连接到变量 ta 中

sprintf(ta,"%s+%s",ta,tb);

我得到字符串 1+2。但我需要在 ta 中存储字符串 2+1 然后我尝试

sprintf(ta,"%s+%s",tb,ta);

但我得到了字符串 2+2+2+2+。我不明白为什么会这样，你能帮帮我吗？下面是完整代码

int main() {
    char ta[5];
    char tb[5];
    sprintf(ta,"%d",1);
    sprintf(tb,"%d",2);
    sprintf(ta,"%s+%s",ta,tb);
    //sprintf(ta,"%s+%s",tb,ta); uncomment for the second case
    printf("taid:%s",ta);
}

最佳答案

sprintf(ta,"%s+%s",ta,tb);
sprintf(ta,"%s+%s",tb,ta);

调用 sprintf 的两行都有未定义的行为。您正在尝试将 ta 复制到 ta 本身。

C11 §7.21.6.6 The sprintf function

The sprintf function is equivalent to fprintf, except that the output is written into an array (specified by the argument s) rather than to a stream. A null character is written at the end of the characters written; it is not counted as part of the returned value. If copying takes place between objects that overlap, the behavior is undefined.

关于c - Sprintf 函数 + 顺序参数，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/29997645/